我们可以说他knowledgeable（有见识的；知识渊博的）

She's very knowledgeable about art.

她对艺术很在行。

Graham's very knowledgeable about wines.

格雷厄姆对葡萄酒非常了解。

或者an expert on（某方面的专家），

He's an expert on ancient Egyptian art.

他是古埃及艺术的专家。

He considers himself an expert on the subject.

他自认是这学科的专家。

或者know all about（对此了如指掌）：

I know all about being poor.

我太了解贫穷了。

A friend is someone who knows all about you and still loves you.

朋友是一个对你了如指掌却依然爱你的人。

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.

事实是，我永远不可能了解关于你的一切，就像你永远不会知道关于我的一切一样。

有时候我们也可以说某人knows a thing or two about（略知一二）。

但是，大家懂得，说得越轻描淡写，越自信，绝不意味着他们真的只“略知一二”:

My name is Jester, and I know a thing or two about this place.

我叫杰斯特，我对这个地方略知一二。

Jack knows a thing or two about kids. He's got five.

杰克对孩子略知一二。他都有五个孩子了。

如果有人是专家，他们know what they're talking about：

She knows what she's talking about.

她知道自己在说什么。

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.

我在这里长大，我对这个地方了如指掌。

He's a taxi driver, so he knows London like the back of his hand.

他是个出租车司机，所以他对伦敦了如指掌。

2，如果一个人对某一事物不懂

如果有人对某一事物一窍不通，

他们don't have a clue（不知道，毫无头绪）：

I don't have a clue where she lives.

我不知道她住在哪里。

Don't ask him to do it-he doesn't have a clue!

别让他做,他对此一窍不通！

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.

我对照顾孩子一窍不通。

I'm afraid I don't know the first thing about cars.

恐怕我对汽车一窍不通。

如果你理解不了，

你don't get it（不明白，不懂）：

You just don't get it! People avoid you because you offend them.

你就是不明白！人们避开你是因为你老得罪他们。

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.

我就是搞不懂这些税单。

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.

这个解释我根本无法理解。

二、会/不会做事

1，如果懂怎么做，

可以说他们know how to do it：

I don't know how to do it.

我不知道怎么做。

You never knew how to do anything else.

你从来不知道怎么做其他的事。

或者他们 are good at it（擅长）:

I've never been very good at drawing.

我从来不擅长画画。

She's very good at motivating her students.

她很善于激励学生。

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.

她很擅长应付难搞的客户。

Robin is an expert at cheesemaking.

罗宾精通制作奶酪。

He's a genius at organizing people.

他是个善于组织。

2，如果不懂怎么做，

就说他们are no good at it：

I'm no good at speaking in public.

我不擅长在公共场合讲话。

I'm no good at dancing - I always get hopelessly out of step.

我不擅长跳舞-我总是合不上拍。

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.

我不知道国庆假期怎么过。

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