Translation:What do you want me to think about them?
Pensar can change prepositions. For instance, when “pensar” substitutes “achar“, it borrows the latter's prepositions. Also, when you think something of or about something:
Eu penso nele. “I think of him”. Very straightforward. That's when “pensar em/no/na” should be used.
Eu penso coisas ruins sobre ele. “I think bad things about him”. Thoughts of speculation, expectation or even complete fantasy.
Eu penso coisas ruins dele. “I think bad things of him”. An opinion. “Penso” could be changed for “acho”.
Both "em" and "sobre" can be used with subtly different meanings: http://dictionary.reverso.net/portuguese-english/pensar
On a related note, and after perusing through that link, I have to say that I've never seen "pensar" used in the sense of "to bandage, to dress (a wound)". At least over here people will use "pôr/colocar o penso". This dictionary accepts it (definition 11.), but I wonder if anyone could tell me if "pensar uma ferida" is somewhat more common in Brazil in colloquial language. Thanks in advance.
I never ever heard that here in Brazil. I think it's a thing from Portugal. As I read in here (http://www.priberam.pt/dlpo/penso). It's definitely not common here in Brazil. We say "colocar/pôr bandeide" or "bandeige" (it varies depending on the accent). If you search on Google for "pensar uma ferida", the few results are all in PT-PT. Maybe it's something lost its usage with time.
I assume that's a question, so here are a few links for conjugation websites:
- https://conjuguemos.com/list.php?type=verbsdivision=verbslanguage=portuguese (Portuguese verb conjugation games - you should use this website after you feel to get a hang of the rules)
Our very own Davu wrote a few articles about verb conjugation on the forums: