How does Iago try to silence Emilia in "Othello"?
He doesn't really speak to her much at all during the play itself, which says something in itself: in fact, the only real conversation which Shakespeare dramatises between them is when she has stolen the hankerchief for him - and then, he's very dismissive: he gets the hankerchief, and then tells her to leave.
Of course, Emilia doesn't actually know the details of Iago's plan, and it's only when Othello murders Desdemona that she actually starts to speak out - and this is when Iago has to try and silence her. Look at the way his blunt, sharp utterances become more urgent:
IAGO: With Cassio, mistress. Go to, charm your tongue.
IAGO: What, are you mad? I charge you, get you home.
IAGO: ’Zounds! Hold your peace.
IAGO: Be wise, and get you home.
And it is after thsi last line that Gratiano tells us that Iago has drawn his sword to threaten Emilia - and, within a few lines, he has stabbed her with it. When words fail, when Emilia refuses to listen to his orders, he plays his final card, and silences her by killing her.