sound someone out
phrasal verb with sound verb uk/saʊnd/ us/saʊnd/
试探（某人）的看法，探（某人）的口风
to discover informally what someone thinks or intends to do about a particular thing, so that you can be prepared or take suitable action
Perhaps you could sound the chairwoman out before the meeting, to see which way she's going to vote? 也许在开会之前你可以探探主席的口风，看她打算投哪一方的票？