Allergies and fragrances are indeed a problem for some poor guys like you and me. Gucci Envy was the first fragrance I purchased, but I had to sell it after a few weeks because I noticed, that I got serious allergic reactions in form of asthmatic spasm.
Actually my interest in perfume started after this, cause I started to sniff all kinds of fragrances, trying to find out which components I react to (and of course enjoying a lot of different fragrances).
Now to your question: the easiest way to find out, if you are allergic to Gucci pour homme, is to get a sample and where it several times, you'll notice allergic reactions.
It is not easy to find out specific allergic components, because people can be allergic to almost everything and only a small part of a perfumes components is listed on the box. These are however the most potent and common allergic components (like isoeugenol, cinnamal, oakmoss, treemoss...). Allergic reactions also depend from the amount of the allergen you're exposed to. So trial and error is the way to go.
Allergologists can test almost every substance if you ask them to. After that you'll perhaps know, that you're allergic to everything. The result of those tests and you're reactions to the substance in nature or fragrance are however only partially correlated.
So, don't give up easily, there are a lot of fantastic fragrances out there, that will work fine with your nose or whatever problems you got.