All characters except a druid, monk, or wizard is proficient with all simple weapons. In NWN2 a character cannot wield a weapon they do not have the proficiency for.
Some simple weapons are:
- Dagger
- Mace, heavy
- Mace, light
- Club
- Morningstar
- Spear
- Quarterstaff
- Dart
- Crossbow, light
- Crossbow, heavy
- Sling
See here for a full list.
D&D Comparison
In DnD 3.5 a character takes a -4 penalty to attack rolls when using a weapon she/he is not proficient with.