How to detect warlock 'Create Thrall' effect?

Question

The Great Old One patron give the ability Create Thrall

Create Thrall

At 14th level, you gain the ability to infect a humanoid’s mind with the alien magic of your patron. You can use your action to touch an incapacitated humanoid. That creature is then charmed by you until a remove curse spell is cast on it, the charmed condition is removed from it, or you use this feature again.

You can communicate telepathically with the charmed creature as long as the two of you are on the same plane of existence.

My question is simple: How can you detect this condition? Does a detect magic or true sight spell work? (The ability does not say it is magic, or even a spell). Any other method?

Answer 1

Detect Magic will work

As you've quoted, the first sentence of Create Thrall specifically states it is magic(my emphasis):

At 14th level, you gain the ability to infect a humanoid’s mind with the alien magic of your patron.

It is clear that this is magic, and should therefore be detected by detect magic.

For the duration, you sense the presence of magic within 30 feet of you.

But what will it say?

Unfortunately, not much RAW, just that there is magic there. It'll be up to the players/DM to determine if anything more is disclosed and what that would be - or provide clues towards that if they don't want to outright disclose it in entirety.