Do I still add sage?
I guess the answer to you is that we really can't give you one perfect answer.

The recipe is sort of vague. It calls for "sage" rather than "dried sage" or "fresh sage" and it doesn't specify a brand of "Italian seasoning", so there's no way to know whether or not theirs included sage already.

So, I'd ask myself a couple of questions:


How far down the ingredients list is sage in my Italian seasoning. 


In a list of, say six ingredients, is it second or last? Or, are there twelve ingredients and it's tenth? Remember that ingredients lists are required to be listed from highest percentage to lowest. If it's high up the list, I'd be tempted to omit the sage. If it's really low down on a relatively long list, I'd guess that there's very little actual sage in the seasoning and go ahead and use the full amount in the recipe. If it's in the middle, use half.


How much do I like sage?


Sage can be a very strong ingredient, so it's understandable if you don't like it. If that's the case, I'd be more likely to leave it out. However, if you like sage, use it.



If I had to guess, sage is going to be pretty low on your ingredients list, so my general recommendation based on the information I have is that you use somewhere between half and all of the sage as listed in the recipe's ingredients and hope they mean dried sage because if they mean fresh, it's going to be really strong (dried herbs are much stronger than fresh herbs).

If you really aren't a fan of sage, leave it out entirely! It's not going to hurt anything one bit.