I didn't study at uni but I've got a secondary school diploma.
Is it an A- Level or a GCSE equivalent?

See a translation

Presumably A-level equivalent if you got it when you were ~18. According to English universities, the Italian qualification that's equivalent to A-levels is the Diploma Di Esame Di Stato, with different percentages being equivalent to different A-level results.

If that's what you have or what you have is above that, then it's A-level equivalent. I obviously don't know how the Italian education system works, though, so if you're unsure you should contact the relevant people if you were wanting to apply for a specific course that required A-level or GCSE-equivalent qualifications .