Lightning Lure says (among other things):
The target must succeed on a Strength saving throw or be pulled up to 10 feet in a straight line toward you…
"In a straight line" here leads to an interesting question. If there's a hole in the floor between you and the pulled creature, will the creature be pulled over it as though Lightning Lure had created a tiny Star Trek tractor beam? That is a straight line, after all. Or will the creature fall through?
One situation when this might be relevant is if you want to immediately pull an ally (who doesn't mind a little friendly fire) over a small gap instead of waiting for them to jump on their turn.
Best Answer
Ask your DM
This is not explicitly specified in the description of the spell, or the rules. It will depend on how your DM interpret the spell description if you do a 10-ft pull and a hole is between the caster and target.
What I would do: resolve the spell as up to 10-ft pull, regardless of terrain. If after resolving the target ends up on a tile with a hole, it will fall.
This interpretation is more based on simplicity and intuitive interpretation by my group.
If your player wants to tactically pull a target into the hole, instead of pulling it 10-ft, just pull it 5-ft, then it will fall into the hole and we don't need to question what would happen.