Final purpose is to make sure ROS_PACKAGE_PATH environment variable includes the directory your source code in.
check it as follow
$ echo $ROS_PACKAGE_PATH /home/youruser/catkin_ws/src:/opt/ros/kinetic/share
In my case, the ROS_PACKAGE_PATH is still /opt/ros/kinetic after operating as described in the tutorials. It works after I lauch the ROS app with roslaunch xxx.
2. CLion config
It works in 2020.01.