Do you think Socrates gave a solid opinion about justice? If not, why?

We do not have any writings of Socrates himself preserved. Instead, we have reports about Socrates in the works of Plato, Xenophon, Aristophanes, and later writers. There are many different opinions about justice that are attributed to Socrates in these works, and thus it is unclear precisely which of these opinions you are being asked to comment on. Also, you are being asked by your instructor for your own opinion, which depends not just on information about Socrates but your own personal conception of what is just.
One of the most interesting points about justice attributed to Socrates by Plato is the notion that it is better to be the victim of an injustice than one who commits an injustice. Socrates, in Gorgias, argues that one who suffers an injustice (such as the victim of a robbery) only loses material goods, a temporary loss that affects the least important things in our lives, while a person who commits an injustice injures his or her own soul, a far deeper and more lasting form of harm. As to whether you agree with this, it will depend on the relative degree to which you value external goods versus moral character. 
Another interesting point you might consider is found in Crito, in which Socrates argues that one should obey the laws of one's city even if they are unjust. He argues this point in terms of the debt one owes to the laws and the civic society they enable. This again is a point on which your opinion will depend on your own ideas and experience; there is no right or wrong answer here as philosophers have taken both sides on the question.