There is an easy way. Taking this “Hide Bone by Name” blueprint node as an example:
Go to you code editor and go to the “Find in files” feature:
(Screenshot example with Rider here, but Visual Studio also has this feature in Menu bar → Edit → Find and Replace → Find in Files)
Finally TYPE the name of the function as seen in the blueprint node but WITHOUT SPACES
(The Blueprint Node displays spaces between the words of the function to make things look nice)
The search results of the Find in Files feature reveals the whereabouts in the C++ Unreal library 
Double click the line in the search result that matches what you are looking for and it will open the file in question revealing the full path.
Now you can include the .h file in your code and call the function
