Like, (1) the in-game help says that in the cases of a successful surprise attack "a yellow exclamation mark will briefly appear on top of the enemy you just struck". I never see such an exclamation mark. The only time I often see an exclamation mark is *before* an attack, apparently to indicate that the enemy has noticed me. Even if I wait behind a closed door and hit an enemy who comes through that door (which the in-game help describes as one way of executing a surprise attack), I still see no visual clue that I executed a successful surprise attack.
I think a new forum post is as good of a place to ask questions as elsewhere.
Ad 1. I feel like you executed a surprise attacks like you wanted to, you just most likely missed a (very brief) visual indication - the exclamation mark for surprise doesn't appear over enemies like the notice mark, but rather is layered on top of the enemy. You can see the difference in this hitless playthrough at 0:08 by Supernewb52 - notice the difference between when the rat wakes up, and when it is attacked while crossing the door - a yellow streak (exclamation mark) does indeed appear.
Anyway, next question (2): In the main UI, right below the square box in the top left corner (showing my character), I see a small, gray disc that spins on every move. My guess is that it's relevant when fighting a slower enemy, with me having multiple moves for a single move of his, but it's not clear to me what it means *exactly*.
And (3), why can't I find this Fandom through the Android Fandom app?
This indicator is only used to display Hero actions, not enemies; you can find some informations on it on the stats page. Now to be fair there isn't that much meat on that page just yet, but what you should know is that it can be used to roughly determine the upgrade level of unidentified items, or know how much time your actions take exactly since it shows incomplete/overflowing turns.
But as for the 3 - I have no idea, I have never used this app. It could be that this wikia is not optimised for mobile enough, for some reason? Hard to tell, I'll try investigating.