She's very knowledgeable about art.
Graham's very knowledgeable about wines.
或者an expert on（某方面的专家），
He's an expert on ancient Egyptian art.
He considers himself an expert on the subject.
或者know all about（对此了如指掌）：
I know all about being poor.
A friend is someone who knows all about you and still loves you.
或者know all there is to know about（知道所有关于它的知识）：
Truth is, I'll never know all there is to know about you just as you will never know all there is to know about me.
有时候我们也可以说某人knows a thing or two about（略知一二）。
My name is Jester, and I know a thing or two about this place.
Jack knows a thing or two about kids. He's got five.
如果有人是专家，他们know what they're talking about：
She knows what she's talking about.
如果有人对一个地方非常了解，他们know it like the back of their hand（非常了解，了如指掌）：
I grew up here; I know the place like the back of my hand.
He's a taxi driver, so he knows London like the back of his hand.
他们don't have a clue（不知道，毫无头绪）：
I don't have a clue where she lives.
Don't ask him to do it-he doesn't have a clue!
或者他们don't know the first thing about（一窍不通）：
I don't know the first thing about looking after children.
I'm afraid I don't know the first thing about cars.
你don't get it（不明白，不懂）：
You just don't get it! People avoid you because you offend them.
或者你can't get your head around it（搞不懂；搞不明白）：
I just can't get my head around these tax forms.
也可以这样说：it's (way) over one's head（太难了；理解不了）:
The explanation went completely over my head.
可以说他们know how to do it：
I don't know how to do it.
You never knew how to do anything else.
或者他们 are good at it（擅长）:
I've never been very good at drawing.
She's very good at motivating her students.
也可以使用相当于be good at的表达方式，它们全部使用介词at:
be brilliant at, be an expert at, be a genius at:
She's brilliant at handling difficult clients.
Robin is an expert at cheesemaking.
He's a genius at organizing people.
就说他们are no good at it：
I'm no good at speaking in public.
I'm no good at dancing - I always get hopelessly out of step.
也可以说某人hasn't got a clue on how to do something（不知道该怎么做）：
I haven't got a clue on how to spend the National Day holiday.