Answered

Add a relative pronoun where necessary:

John, ________ I know very well, is going out with Mary.
A greengrocer’s is a shop ________ you can buy vegetables.

Sagot :

Mizuviz
John, whom I know very well, is going out with Mary.
A greengrocer's is a shop which you can buy vegetables.

Not sure about the second one. But I'm sure that it is not "where" because "where" is not a relative pronoun.

--Mizu
Jers15viz
John, whom I know very well, is going out with Mary.
A greengrocer's is a shop, where you can buy vegetables.

Hope this helps =)