It's next to the Mongolian restaurant.
在蒙古餐馆的隔壁。

A How was your dinner last night? Was it a good restaurant?

A 你昨晚的晚餐怎么样？那家餐馆好吗？

B Yes, it was very good. I really like Vietnamese food.

B 是的，非常好。我非常喜欢越南菜。

A Sounds good. I'd like to try it. Where is the restaurant exactly?

A 听起来不错。我也想尝一尝。那家餐馆的确切位置在哪里？

B Well, you know that Mongolian restaurant we went to last week?

B 哦，你知道我们上周去的那家蒙古餐馆吧？

A Yes, is it near that?

A 是的，离那里很近吗？

B Yes, it's beside it. It's next to the Mongolian restaurant.

B 是的，就在它旁边。在那家蒙古餐馆的隔壁。

Notes 注释

1 There are many ways to specify a location or position, e.g. beside / beside; next to / next to; It's next to the Mongolian restaurant. / It's next to the Mongolian restaurant.

要指出确切的地点或者位置有很多种方法，例如：beside / 在…旁边； next to / 在…的隔壁；It's next to the Mongolian restaurant. / 在那家蒙古餐馆的隔壁。

2 You can also ask about the position of a place or something by saying: Is it near . . .? / Is it near . . . ? e.g. Is it near the restaurant? / Is it near the restaurant?; Is it near the hotel? / Is it near the hotel?

你还可以这样问某个地点的位置：Is it near . . .? / 它在 . . . 的附近吗? 例如: Is it near the restaurant? / 它在那家餐馆的附近吗？； Is it near the hotel? / 在旅店的附近吗？

Key phrases and sentences
重要的短语和句子

How was your dinner last night? Was it a good restaurant?
你昨晚的晚餐怎么样？那家餐馆好吗？

Yes, it was very good. 
是的，非常好。

I really like Vietnamese food.
我非常喜欢越南菜。

Sounds good.  I'd like to try it.
听起来不错。我也想尝一尝。

Where is the restaurant exactly?
那家餐馆的确切位置在哪里？

Well, you know that Mongolian restaurant we went to last week?
哦，你知道我们上周去的那家蒙古餐馆吧？

Yes, is it near that?
是的，离那里很近吗？

Yes, it's beside it. 
是的，就在它旁边。

It's next to the Mongolian restaurant.
在那家蒙古餐馆的隔壁。