Several *Dragonlance* books make reference to gnomes, but the first one that came to mind here was [*The Siege of Mt. Nevermind*][1], 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][2] 

* The collector's edition of the [*Legends* trilogy][3]. 

* The [*War of Souls*][4] 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.

  [1]: http://www.amazon.com/Siege-Mt-Nevermind-Dragonlance-Chaos/dp/B00BUWLBZA/ref=sr_1_2?s=books&ie=UTF8&qid=1452370993&sr=1-2&keywords=chaos%20war%20dragonlance
  [2]: http://www.amazon.com/Dragonlance-Chronicles-Dragons-Twilight-dragons/dp/0140115404/ref=pd_sim_14_8?ie=UTF8&dpID=51lCUdvyQAL&dpSrc=sims&preST=_AC_UL160_SR100%2C160_&refRID=1WF74YQPC9VB06TR3JSR
  [3]: http://www.amazon.com/Dragonlance-Legends-Omnibus-Twins-Fantasy/dp/0140126988/ref=sr_1_fkmr0_2?s=books&ie=UTF8&qid=1452371042&sr=1-2-fkmr0&keywords=chaos%20war%20dragonlance%20omnibus
  [4]: http://www.amazon.com/War-Souls-Dragonlance-Omnibus/dp/0786957158/ref=sr_1_fkmr0_1?s=books&ie=UTF8&qid=1452371042&sr=1-1-fkmr0&keywords=chaos%20war%20dragonlance%20omnibus