In Act I, scene ii of Othello, what is Othello's answer and what does it suggest about what Othello values when Iago warns Othello about Brabantino?
Iago warns Othello that Brabantio is "much-loved" and may try to separate him and Desdemona.
Iago, as your question indicates, gives rise to the way in which Brabantio is popular and the power that he has. In addition to being "much loved" he also, according to Iago, has a "voice potential / As double as the duke's." Basically, Iago is trying to reinforce that Brabantio is definitely not a man without any contacts or influence, and therefore he is not an enemy to cross. However, let us look at how Othello responds to Iago's concern and what that reveals about his character:
Let him do his spite;
My services, which I have done the signiory,
Shall out-tongue his complaints. 'Tis yet to know--
Which, when I know that boasting is an honour,
I shall promulgate--I fetch my height and being
From men of royal siege, and my demerits
May speak unbonneted to as proud a fortune
As this that I have reached.
Othello is very confident in what he has already achieved and his exploits that he has done on behalf of the "signiory," and also he is proud of his lineage and his background and the "fortune" that he has gained. Othello comes across in this speech as a very confident man, confident in his own abilities and powers and in what he has achieved. Just as Brabantio is not friendless, so Othello himself has gained influence and he believes that his exploits will "out-tongue" any of the complaints that Brabantio might raise against him.