"Does he use his brain?"

Translation: Czy on używa mózgu?

[Kendra800150]

"Czy używa mózgu?"

[alik1989]

Seems fine, added.

[Yola448704]

Does he use his brain? - Czy on myśli/ Czy on się zastanawia (co robi)?

[golden.plover]

The brain is in the Genitive case, not Accusative.

[Jellei]

That is correct. "używać" is among those verbs that always take Genitive.