ddynamic_reconfigureConfig.cmake
ddynamic_reconfigure-config.cmake
Maybe it passes the test based on some cached build, but this is clearly a broken dependency link.
A couple of changes happened.

The folder ddynamic_reconfigure was removed in favor of the newly released debian package ddynamic_reconfigure.
The folder realsense2_camera was split to realsense2_camera and realsense2_description, for reducing the package basic size.
Therefor, the fix for the error is

apt-get update apt-get install ros-kinetic-ddynamic-reconfigure
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I had the same catkin build error as tanismar, and ran:

sudo apt-get update

sudo apt-get install ros-kinetic-ddynamic-reconfigure

Then I get the following error:

Err:1 http://packages.ros.org/ros/ubuntu xenial/main amd64 ros-kinetic-ddynamic-reconfigure amd64 0.2.0-0xenial-20190325-154841-0800

404  Not Found [IP: 64.50.233.100 80]

E: Failed to fetch http://packages.ros.org/ros/ubuntu/pool/main/r/ros-kinetic-ddynamic-reconfigure/ros-kinetic-ddynamic-reconfigure_0.2.0-0xenial-20190325-154841-0800_amd64.deb  404  Not Found [IP: 64.50.233.100 80]
I am testing with a D435 and T265, both now working in the Realsense Viewer after I upgraded the firmware on the D435 to 05.11.01.100. The T265 didn't require any firmware update (Just FYI).
Ubuntu 16.04LTS 64-bit

Intel® Core™ i7-6700TE CPU @ 2.40GHz × 8

Intel® HD Graphics 530 (Skylake GT2)

8GB memory

When running the following commands, I get...

command:  modinfo uvcvideo | grep "version:"
version:        1.1.2.realsense-1.3.5

srcversion:     3286F64D5B1431E64E8C37C
command:  sudo apt-get update

Ign:1 http://dl.google.com/linux/chrome/deb stable InRelease

Hit:2 http://dl.google.com/linux/chrome/deb stable Release

Hit:3 http://us.archive.ubuntu.com/ubuntu xenial InRelease

Hit:4 http://archive.canonical.com/ubuntu xenial InRelease

Get:5 http://security.ubuntu.com/ubuntu xenial-security InRelease [109 kB]

Get:7 http://us.archive.ubuntu.com/ubuntu xenial-updates InRelease [109 kB]

Hit:8 http://packages.osrfoundation.org/gazebo/ubuntu-stable xenial InRelease

Get:9 http://packages.ros.org/ros/ubuntu xenial InRelease [4,678 B]

Hit:10 http://linux.teamviewer.com/deb stable InRelease

Hit:11 http://realsense-hw-public.s3.amazonaws.com/Debian/apt-repo xenial InRelease

Hit:12 http://linux.teamviewer.com/deb preview InRelease

Hit:13 http://us.archive.ubuntu.com/ubuntu xenial-backports InRelease

Err:9 http://packages.ros.org/ros/ubuntu xenial InRelease

The following signatures couldn't be verified because the public key is not available: NO_PUBKEY F42ED6FBAB17C654

Fetched 223 kB in 1s (186 kB/s)

Reading package lists... Done

W: An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: http://packages.ros.org/ros/ubuntu xenial InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY F42ED6FBAB17C654

W: Failed to fetch http://packages.ros.org/ros/ubuntu/dists/xenial/InRelease  The following signatures couldn't be verified because the public key is not available: NO_PUBKEY F42ED6FBAB17C654

W: Some index files failed to download. They have been ignored, or old ones used instead.
          
A new GPG keys were deployed for packages.ros.org.

Follow the instructions here

In short, do the following:

sudo apt-key adv --keyserver 'hkp://keyserver.ubuntu.com:80' --recv-key C1CF6E31E6BADE8868B172B4F42ED6FBAB17C654

sudo apt-key del 421C365BD9FF1F717815A3895523BAEEB01FA116

And now try

sudo apt-get update

again.

After that install ddynamic_reconfigure package.
          
@doronhi

Thank you for the updated key. Still getting an error on update:

W: The repository 'http://realsense-hw-public.s3.amazonaws.com/Debian/aptrepo xenial Release' does not have a Release file.

N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use.

N: See apt-secure(8) manpage for repository creation and user configuration details.

E: Failed to fetch http://realsense-hw-public.s3.amazonaws.com/Debian/aptrepo/dists/xenial/main/binary-amd64/Packages  403  Forbidden

E: Some index files failed to download. They have been ignored, or old ones used instead.
          
I am getting that error too and I did your steps.

CMake Error at /home/arl/catkin_ws/devel/share/ddynamic_reconfigure/cmake/ddynamic_reconfigureConfig.cmake:113 (message): Project 'ddynamic_reconfigure' specifies '/home/arl/catkin_ws/src/realsense/ddynamic_reconfigure/include' as an include dir, which is not found.  It does neither exist as an absolute directory nor in '/home/arl/catkin_ws/src/realsense/ddynamic_reconfigure//home/arl/catkin_ws/src/realsense/ddynamic_reconfigure/include'. Report the problem to the maintainer 'Noam Dori <[email protected]>' and request to fix the problem. Call Stack (most recent call first): /opt/ros/kinetic/share/catkin/cmake/catkinConfig.cmake:76 (find_package) realsense/realsense2_camera/CMakeLists.txt:8 (find_package) 
          
The message you posted states "Report the problem to the maintainer 'Noam Dori [email protected]".

It seems that you have cloned ddynamic_reconfigure from a wrong source. If you indeed in a need to build that package yourself and not use apt-get install, try cloning the package from here
          
Yes,I cloned it by myself and not by apt-get and it is work.

It will be better to update it from the apt and not clone it every time.

          
I am also running ROS melodic on ubuntu 18.04.2, tried to build the ROS node source 2.2.6, ran into the same issue (ddynamic_reconfigure was missing from catkin_ws/src), cloned it from https://github.com/pal-robotics/ddynamic_reconfigure, and everything build smoothly then. Thanks for the help here.
Hi @dorodnic ,

I followed your steps by installing ddynamic_reconfigure package, and checking out tag 2.2.6, and run into the same error as ARLVOL. If it is installed from a wrong source, means that the default source is wrong. Can this be fixed? thanks!
What do you mean by "default source"? The realsense2_camera does not state a source for ddynamic_reconfigure.
          
I have the same issue and do not know how to solve ...
@doronhi

Hi, if you see realsense-ros/realsense2_camera/CMakeLists.txt it shows "ddynamic_reconfigure" is required now in line 18. Should I simply remove that requirement, since you said reansense does not rely on it long time ago?
@PhilippeRerole

Hi, did you do any extra operation after cloned and installed ddynamic_reconfigure from gihub?

I have cloned source, compiled then installed, but the same error pops again.
Thanks guys!
          
Sorry for misleading anyone. I didn't mean that "ddynamic_reconfigure" is not needed. Simply that it is not built by realsense2_camera and that the source code for that package is not included or pointed to by realsense2_camera.
The package "ddynamyic_reconfigure" is needed for building and running realsense2_camera.
Michael Blanton, Jr.