Unfortunately, no single test exists that can give you this answer. A test that claims to be able to diagnose food sensitivities and is commonly available is the food IgG test. This test, offered by various companies, reports IgG levels to multiple foods (usually 90 to 100 foods with a single panel test) claiming that removal of foods with high IgG levels can lead to improvement in multiple symptoms. Some websites even report that diets utilizing this test can help with symptoms of irritable bowel syndrome, autism, cystic fibrosis, rheumatoid arthritis and epilepsy.
It is important to understand that this test has never been scientifically proven to be able to accomplish what it reports to do. The scientific studies that are provided to support the use of this test are often out of date, in non-reputable journals and many have not even used the IgG test in question. The presence of IgG is likely a normal response of the immune system to exposure to food. In fact, higher levels of IgG4 to foods may simply be associated with tolerance to those foods.
Due to the lack of evidence to support its use, many organizations, including the American Academy of Allergy, Asthma & Immunology, the Canadian Society of Allergy and Clinical Immunology and the European Academy of Allergy and Clinical Immunology have recommended against using IgG testing to diagnose food allergies or food intolerances / sensitivities.