It seems that the ability to think can be used to find out truths & evaluations about subjects that are not directly observable at the moment. If so, this kind of an ability would be priceless in planning, analysis and deduction. And - if one dares to propose such a statement - it can even be used successfully on subjects we have no prior experience of.
Certainly this is better than the lack of thinking, which is known to cause directionlessness, stick-to-that-ive-ness, incoherent world view, fantasy, delusion, escapism, and voting for that really stupid political party. (You know the one).
Yeah, thinking seems great! Hooray!
Now, what should we think? You? Me? Anyone?
Imagine that someone had lived their life without really thinking about anything. Now a genie in a bottle grants them - not what they want, which is wild sex, fame and riches, but - the ability to think for one day. Yeah, one day and then it's over. That someone is cursing the sadistic genie for granting a useless wish. You come to comfort them, with the intent to courage them to try their new ability and take it for what it's worth. It'll be something for them to remember.
So, what would you advice them to think about?