Is anybody else having an issue where the skill "Learning" in M&M 7 has no effect? Thank you!

I've never heard of the skill being completely ineffective. How have you tested this?

If you mean that it's not giving you extra XP to the one you already have, then that's intentional. Unlike Bodybuilding and Meditation, Learning doesn't work retroactively, meaning it will only give you extra XP to any new XP you get.

Am I right in thinking Learning is meant to increase the XP from killling monsters, but NOT the round 000s of XP awarded for quests?

Yes.

I was monitoring the XP gains of my characters with the skill vs. those without and saw no difference. This was comparing after large clearings of monsters.

If the monsters were very weak, there may be no noticeable difference because Learning is percentage based.

Also, did you control for who was alive and who was unconscious/dead/petrified/etc? Characters under certain status conditions do not gain experience, so the other characters gain more XP (because fewer people are splitting the XP). If your sorcerer kept getting knocked out before the monsters died, but your knight was always active during the kills, the your knight may have kept up with the sorcerer in XP.

If your main point of reference is the Dragonflies on Emerald Isle, the weakest of them only give a total of 24 experience (which, divided by four active party members, is 6 each). I don't think the 10% EXP bonus from Basic Learning at level 1 applies to amounts of experience less than 10.

Fire and Queen Dragonflies, on the other hand, give 56 and 144 total experience respectively, which comes to 14 or 36 when divided among four party members. Those who have Learning should be getting 15 or 39 experience from each Fire or Queen Dragonfly, assuming that you're keeping everyone alive and conscious for the kills.

my 7 learning master (+20 bonus from items) cleric is behind of the 3 monks that have no learning in terms of XP so i'd say its safe to assume that it either doesn't work at all or the xp bonus is so small it doesn't matter at all.

Or that your cleric has been unconscious during the fights, and therefore hasn't gotten a share of the experience.

Only characters that are active (i.e. not Unconscious, Paralyzed, Asleep, Stoned, Dead, or Eradicated) gain experience when a monster is killed.

EDIT: I just checked whether Learning works as intended by having my party (one character with 1 Basic Learning and three characters with 7 Master Learning) defeat a Troglodyte Drone. The character with 1 Basic Learning gained 46 experience from that kill, and the other three characters gained 54 experience. This appears to indicate that Learning does indeed work as intended, and that any evidence to the contrary might be better explained by other factors.