nothing. multiclassing wizard drops your DCs and high DCs is one of the strengths of the class (along with flexibility). Since you should be maxing int, and pumping a lot of build points into con, and not dumping strength, getting your dex high enough for evasion to do you any good means you are compromising something important.
A monk's main stat is wisdom, which is more or less a dump stat on a wizard so there's no synergy.
If you are going to multiclass a wizard for evasion, go rogue. Int is a secondary class ability for rogue, so you'll be able to get full trap/umd/search skills with 2 levels of rogue, and all the skill points you'll have to burn with a high int. _much_ better synergy, more skill points and you'll still have evasion. Even though rogue is a much better idea than monk, I'm personally against multiclassing wizard. It's the only class I wouldn't consider multiclassing. The capstone is too good, and having uber DCs equalizes the end game between sorc and wizard. A wizard multiclass is just a slower version of sorc with less spell points, less damage, lower dcs and trap skills.
People think multiclassing monk with anything is a great idea and it's not really. In some cases it's simply not the class to splash with, and a wizard multiclass is one of them. A cooking analogy: like putting paprika, chili powder and black pepper on ice cream.
"Monk" shouldn't be used in the same sentence as "wizard".
Just build a melee then!Wizards enchantment and necro spells work more reliably in end game, though a sorcs work well too, just not as well. A sorc does higher damage when nuking elemental style, and has more raw power. Wizard is more of a finesse class.
A wizard can freely swap out spells, has more spell slots, but casts slower and has less spell points, which is offset by higher DCs. If it works the first time, it doesn't matter if you are a little slower.
There are workarounds whether you go sorc or wizard to boost up their weaknesses. It's really a matter of personality and preference. Saying one is better than the other is disingenuous. It depends on whether you like to nuke or instakill/enchant.
Nuking is better for bosses, instakills/enchant is better for handling large numbers of trash mobs. Wizards have more utility, sorcs do more damage.
Like I said though, there are ways to boost up your weaknesses no matter which way you go and you can debate one over the other all day long.