Entity Riding Detection

I have been working on a moving upwards and downwards entity.  I used some keybinds and figured out how to control the entity's vertical position (by changing the vector).  I have tried to find it on the forums and on youtube, but I was unable to find a method to track what entity the player is riding.  I did some tests as well, but nothing I do seems to work because idk how to program most of this stuff.  How do I detect what type of entity the player is riding?  Thanks