Can I try this on?
'Provare' — 'pro-VA-re'. Stress on the second syllable. The 'r' is a single tap, not a heavy roll.
The first thing you say before heading to the fitting room. Always ask before taking items — it's polite and staff may help carry items for you.
'Posso' (can I, from 'potere') + infinitive is the go-to permission structure. 'Questo' = this (masculine). Feminine: 'Posso provare questa?' The object pronoun can also be attached: 'Posso provarlo?'
Posso provare questi?
Can I try these on?
Plural — taking multiple items
Vorrei provare questo.
I'd like to try this on.
'Vorrei' is slightly more polite — conditional of volere
È possibile provarlo?
Is it possible to try it on?
Most formal variant
Italian fitting rooms sometimes have item limits, typically 3-6 pieces. A numbered tag may be given to track how many items you've taken. This is standard in chain stores like Zara, H&M and Italian brands like OVS.