What sensitivity in the Logitech Profiler will give me a linear response for my Logitech Momo Wheel?
By linear I mean controller min/max = in game min/max; and not controller 5 deg = in game 5 deg.
So which is it: 0%, 50%, or 100%?

None of the settings in the Logitech profiler have any bearing on linearity at all, they are all related only to force feedback. Linearity would have to be something you set up in your specific games.

What game in particular are you trying to set up?

edit: Oh, unless you're talking about the red MOMO and it has some different settings I've never seen before, in which case I have no idea. When you're given a "sensitivity" option for that sort of thing, generally 50% is linear, but that is in no way universally true.

That's an in-game adjustment.
General starting point for my wheel settings (G27 at least):
check Use special force feedback device settings
Overall effects strength 110%
Sprint effect 0%
Damper 0%
check enable centering spring
centering spring strength 0%
check use special steering wheel settings
UNcheck report combined pedals (except for rare games that need that)
degrees of rotation (personal preference by racing type...I settle on 340 for most though
check use special game settings
check allow game to adjust settings

That's mine for almost all games, sometimes a little variation on strength and rotation.

I opened the Logitech Profiler and left clicked on one of the 3 axis in the list on the bottom left and selected axis properties to get the lower window with the sliders. I am not sure, but I think "sensitivity" is for adding a curve.

Ha! I've never seen that before, and I've been using Logitech wheels for about 12 years now. I suppose I have actually seen that when configuring my Logitech flight stick, but it never occurred to me to try it with the wheel.

You learn something new every day.

In that menu, yes sensitivity would be for curving the output and 50% is linear.