Suppose I suspect that an object is magical. I cast Detect Magic, but I see no magic aura on it.
However, I'm still suspicious, and now I begin to suspect that the aura has been hidden by Nystul's Magic Aura. I happen to have a Gem of Seeing, so I activate it and then once again use my action to see magic auras while peering through the gem at the suspicious object, this time with the truesight granted by the gem, which among other things allows me to "automatically detect visual illusions".
Will the combination of truesight and Detect Magic allow me to see a magic aura hidden by Nystul's Magic Aura, or at least allow me to perceive the presence of an illusion?