он знает, о чём говорит(Coun. Steve Hayes is another councillor whose words are weighty when it comes to Birkenhead's situation. He was taken to the town at age two and he surely knows his onions when he speaks about the town. (YouTube)ART Vancouver)
понимать толк в чём-л.(The expression "know one's onions" means to be very knowledgeable or experienced about something, to know a great deal about a particular subject. (Collins Dictionary) The origin is Cockney rhyming slang: onions = onions rings = things. • He knows his onions. -- Он знает / понимает толк в этих делах.ART Vancouver)
знать толк в (чём-л.)(The expression "know one's onions" means to be very knowledgeable or experienced about something, to know a great deal about a particular subject. (Collins Dictionary) The origin is Cockney rhyming slang: onions = onions rings = things. • He knows his onions. -- Он знает / понимает толк в этих делах.ART Vancouver)