know all the answers
Also, know a thing or two; ; know one's way around. Be extremely knowledgeable or experienced. These idioms may be used somewhat differently, expressing overconfidence, as in Helen always knew all the answers, or thought she did, or competence, as in Bob knows a thing or two about battery technology, or ruefulness, as in I thought I knew it all about plants and then I got poison ivy, or genuine expertise, as in John knows his way around tax forms. The first term dates from the early 1900s, the second from the later 1700s, the third from the later 1800s, and the fourth, also put as know one's way about, dates from the 1500s. Also see know one's stuff; know the ropes; under tricks of the trade.