Yes we had an allergy test some years ago and he is allergic to dust mites, storage mites, grasses, beech trees, dandelions and much more. My vet said food allergy testing is not very accurate and he could also be allergic to several foods so I never had that done. I have just ordered his immunotherapy again which seems to help him with paw nibbling and ears ( i give monthly jabs ). Vet said not to buy big bags of kibble due to dust mites once bag is opened, but surely any size bag is opened daily although I do keep it in an air tight container.
As it is an environmental issue I think immunotherapy is the best option as he is obviously out and off lead in woods most days,but as you say his immune system is being shut down due to Apoquel. My vet said a few years ago that with the monthly jabs many dogs no longer need to stop the itch but it has never completely gone and I feel sorry for him scratching although it isn't constantly.
Thanks for the allergone advice, I will look into that.My vet has recommended a mouse to put on his feet before walks to save washing his feet after every walk.