The easiest way to tell if the quest is a promotion quest is by looking at the rewards in the bottom left-hand corner of the quest in the "My Quests" Interface. It should show a portrait of an upgraded companion as a reward.
"I didn't complete the quests for a couple of my Companions (including El Toro) and now I cannot remember what the quests are!!"
If the companion is high enough to trigger the quest, and you have talked to them in a tavern basement, then you should have the relevant quest in your list of uncompleted quests. As One-Eyed Jack said, you should be able to identify which quest you want by looking at the rewards section of your open quests - you will see a little portrait of the updated El Toro (or whoever) in the relevant one.
"The exclamation point is greyed and I can't find any hints"
The grayed-out exclamation point I think just means you have talked to him in a tavern and activated the quest sequence, but have not completed the series of quests. If for some reason you can identify the correct quest but the yellow quest arrow isn't working, in the bottom right of that quest's box in the open quest screen there will be a voice bubble for you to click on, where you will see all of the relevant dialogue for that quest.