"What do they think?"

[jurgen_maes]

Τι νομίζουν; should be correct too.

[NikosPainnessi]

absolutely

[uSCF10]

βασικά η προσωπική αντωνυμία χρησιμοποιείται μόνο για έμφαση και όχι σε απλές προτάσεις όπως εδώ

[JacobPast177]

What's wrong with Τι σκέφτονται; ?

[Lng52-._]

That's what I would have used as well.

[uSCF10]

Τίποτα :))

[Jon345104]

Τι νομίζουν was marked wrong

[Jon345104]

Would τι αυτοί νομίζουν have the same meaning

[jaye16]

I'm afraid the word order is not correct.

[Daria702360]

It must be the same meaning

[CoranceC]

I had assumed that the pronoun was optional in this case, it seems I was mistaken.

[BillDe]

Why is the pronoun needed? (If it is.)

[G.Georgopoulos]

It's not ;)