know sth inside out
- He knows the system inside out.
be in touch
- He's not really in touch with what young people are interested in.
know your stuff（英式英语以前也用 know your onions）
- Once you know your stuff, you'll look like an expert, too.
have a familiar ring (to it)
- Her name had a familiar ring to it.
- I didn't know who was speaking, but his voice had a familiar ring.
ring a bell
- His name rings a bell but I can't think where we met.
- The description of one of the lads is definitely familiar. It rings a bell.