To ask precisely about something that has been previously mentioned, the French language uses a special word, lequel(here in the feminine and plural form).
Lesquelles = quelles chaussures ?
For grammar lovers:
The word lequel is called an interrogative pronoun in grammar terms. It is used to replace the interrogative word quel + a noun!
Tu as vu mes nouvelles chaussures ?
Quelles chaussures? ⇒ Lesquelles ?
I still don't really understand when to use this...?
Only when you would like to ask precisely about a particular object or person that was just mentioned in the conversation.
For instance?
Imagine we are in a line at the supermarket, waiting to pay, and I say:
L'homme devant nous a acheté beaucoup de choses.
How would I know which man you're talking about?! There might be five men in front of us with a lot of things!
This is why you would ask...?
Lequel! Oh, now I get it!
The interrogative pronoun lequel can also vary according to the gender and number of the noun: