Several Dragonlance books make reference to gnomes, but the first one that came to mind here was The Siege of Mt. Nevermind, part of the Chaos War series. It's almost entirely set in Mt. Nevermind, the gnome city, and it's one of the few books where different gnomes get different personalities.
Unfortunately, as far as I can tell, Chaos War was never released as an omnibus edition. The only multi-volume sets I know of are:
The collector's edition of the original tetralogy
The collector's edition of the Legends trilogy.
The War of Souls omnibus
It's been a while since I read any of these, though I can go dig them out if any of them sound familiar. Tasselhoff Burrfoit has a magical time travel device during Chaos War and War of Souls that sounds decidedly gnomish, so it would make sense for him to visit Mt. Nevermind during one of those series.