You must know Beijing well.
你一定非常熟悉北京。
How many times have you been to Beijing?
你来北京多少次了？
Lot’s of times. Sometimes for business, sometimes for holiday.
很多次了。有时来出差，有时来度假。
You must know it very well now.
你现在对北京一定非常了解了。
Well, I know it better each time I visit.
哦，我一次比一次更了解北京。
That’s good. I think it’s better when you know a city well.
好。我想当你了解一个城市的时候感觉会更好。
Yes. You enjoy it more. It’s more interesting.
是的。你会更喜欢它。它会更有趣。
要问某人做某事做了多少次，你可以说：How many times . . . ? / 多少次 . . . ? 
例如: How many times have you been to Beijing? / 你去过北京几次？
如果你想描述你对某地非常熟悉，比如一个城市，你可以说：I know it better each time I visit / 我一次比一次更了解它。