Lets see if I can stump you with this rules question ktom!

Incognito reads "Attached character loses all Traits and immunities". Does this remove one copy of every trait, or as many as the character has? E.g. if I put this on the Queen Of Thorns and then use Old Nan to give her the House Tyrell trait will both the printed and newly acquired copies of this trait be lost? What if I then attach Rhaegar's Harp to her, will they cancel each other out or will Incognito take away all traits?

Bah! I forgot to check the Rhaegar's Harp discussion on tzumainn's site. Now I see that Rhaegar's Harp and Incognito do in fact cancel each other out, leaving other traits in tact. But I still don't know for sure whether Old Nan can give her back the House Tyrell trait without Incognito taking it. I expect she can't given what you said in the conversation on Rhaegar's Harp:

>>> ...we know that "loses ALL non-immunity keywords" means that cards keep losing as many instances of each and every keyword necessary for them to
functionally not have the keyword. ...

perthius said:

~ Glad you looked at the Harp discussion so I didn't have to make some snide comment about trying to stump someone with a question that has already been answered.

Seriously, though, you have the right of it. Incognito's "loses ALL traits" will trump all effects that give a card a trait (short of Rhaegar's Harp, which will "cancel out" as equal-but-opposite effects). Old Nan cannot overpower it, even if she tries to give a character BACK a printed trait. The easier-to-see parallel example is that if you have Den of the Wolf, it will trump effects like my Tourney for the Hand (even for Knight characters that already have immunity, like Brienne) because it says characters lose ALL immunities.