In Othello, who does Cassio ask to help him get his job back?

He asks Desdemona, but it is at Iago's insistence that he
does this.  In Act II, scene iii, Iago encourages Cassio to "mend [the loss of his
position] for your own good."  And, even though Cassio believes that asking is a lost
cause because Othello will "tell me I am a drunkard," Iago tells him not to give up
hope.  He persuades Cassio to ask Desdemona for help getting his place
back:

Our
general's wife is now the general . . . .  Confess yourself freely to her, importune
her, she'll help to put you in your place again. . .  This brawl between you and her
husband, entreat her to splinter and. . .this crack of your love shall grow stronger
than 'twas before.

Pretty
sound advice, right?  But once Cassio exits, Iago shares his real motives to the
audience:

. .
. Divinity of hell!

When devils will their blackest sins
put on,

They do suggest at first with heavenly
shows,

As I do now.  For while this honest
fool

Plies Desdemona to repair his
fortunes,

And she for him pleads strongly to the
Moor,

I'll pour this pestilence into his
ear,

That she repeals him for her body's lust. .
.

And so, the real turning
point of Iago's scheme has arrived -- the opportunity to convince Othello that his wife
is having an affair with Cassio.