How to find the actual services provided like 'pick_food'?

In section 5 on service clients and servers I understand and have completed the exercise without any problems, I know how to get the node and the argument ‘traj_name’ to use in the first part of the call but I don’t no how to get the valid command it takes like pick_food, release_food , if they had not been provided how would I find them ?

You would need to follow the path of the launch file that’s being launched. But that’s not in the scope of this exercise, so I recommend you just stay with the knowledge that it’s being provided. Just for your information, the services are provided by the node inside the package trajectory_by_name. To find out about this, you can run the command

rospack find trajectory_by_name

which would give you the path to where this package is located, and you can find everything that is being published there.