Where are the fitting rooms?
'Camerini' — stress 'ca-me-RI-ni'. The 'c' before 'a' is hard, like 'k'.
When you have items to try and can't see the fitting rooms. Ask any staff member — they'll point you in the right direction.
'Dove' (where) + 'sono' (are) is the basic location question structure. 'I camerini' — plural masculine, 'camerino' is literally 'little room'.
Dov'è il camerino?
Where is the fitting room?
Singular — when there's only one or you see just one
C'è un camerino libero?
Is there a free fitting room?
When rooms look occupied
Posso usare il camerino?
Can I use the fitting room?
Direct request
In Italy, 'primo piano' means first floor above ground level (what Americans call the 2nd floor). The ground floor is 'pianterreno'. This confuses many English speakers.