A high level paladin has used command on a creature and ordered it to grovel. The creature then falls prone and ends its turn. At this point the paladin has another turn and triggers a reaction from the creature. My question is, is the creature still under the command of the paladin so would it be able to take its reaction?
Spells only do what they say in their descriptions.
Command(ing) a creature to grovel only causes the creature to:
... fall prone and then end its turn
on its next turn. Nothing is said about the creature not being able to take reactions so it is still able to take them, even on the turn that Command was cast.
It's also worth noting the Command only has a duration of 1 round. By the time the Paladin's turn comes up again the spell has ended anyway.