These gnomes are found throughout the Gnomish area of Solusek's Eye. They come complete with pets, and cast the traditional arsenal of Magician spells.
Be well-organised with your partner/group if you are going to go up against this mob when it's about even with you in level. If he starts getting a chance to cast, your chances of defeating him are lessened substantially. Try to pull him before he summons his pet, that'll make it a lot more feasible. I don't think a melee character could solo it unless they were outrageously twinked or way higher in level, especially with the Earth pet he brings along.