I am looking for relatives with the surname di Domenico.
My great grandfather was called Vincenzo and was born about 1885 near Naples.
He then trained in Milan's school of music playing the French horn.
I know his father was called Gennaro ( Jennario).
Unfortunately family records have been lost.
My mother, sister and myself will be travelling to Naples next year to search.
Can anyone help. Thanks.

First you MUST know the name of the town of birth. Near Naples is not good enough.
If he emigrated to the USA you need to find his entry record. If he went to the UK it will be more difficult but if he was alive in 1911 his town of birth may be on the census.
There are some tips on finding the town of birth on my website.