In Combat
As mentioned above, a Medium maneuver (attacker using Ag/Qu bonuses averaged together; defender gaining normal DB). If the result on the maneuver column says 100 or higher, then you have touched the target and get the touching bonus on spells.
Alternatively....
You could use the same modifiers and use the MA Sweeps attack table, and look up the result on the proper AT column of the table. Any non-zero result equals a solid touch (but no damage is actually done on the table itself). I think that this is what DS was suggesting above. The MA Sweeps table is ideally suited due to when/where damage starts based upon the armor worn.
However, I would NOT use any melee skills with this as melee skills are all about damaging the foe, not just touching him. The focus is different and could possibly disrupt the spell depending upon its wording. (Note: some spells could work very well with attacks, working to add extra damage -- the point is that it depends on the spell itself).
Non-Combat Situations
This would depend upon the situation, but in most cases, you likely shouldn't even need a roll if the target is unaware that you are trying to touch him (i.e. if you did roll, you could add in bonuses for surprise, and approach from the rear to get those bonuses, and so forth, putting your total adjustment close to 100 before even rolling. Most rolls would be just to see if target moved unexpectedly just before you attempted to touch him.