How to find a missing track in iTunes? Missing as in, if I do find it and try to do something with it, iTunes will say "The file is not there; want to look for it?"

I suspect there are two of them, because every time I sync iPad, I get two pop-ups of "one item failed to sync, ask iTunes for the reason"  But there are never any pop-ups on iTunes.
iTunes will put an exclamation mark in a circle against any tracks it cannot find the source file for.  It doesn't do it during sync, but if you select all and then Get Info, the ones missing will be flagged.

You could perhaps scroll down &amp; look for that.
View by My Music > Songs if you can't narrow it down to a specific playlist.