Where is the well im supposed to find, is this inside verga or on the outskirts somewhere ?

The well is actually in the burned village. I had to use the guide to do this quest, because the poem makes NO sense. I thought for about 2 hours the well was the well outside of the Vergen Inn, since that is the ONLY PLACE WHERE LOUD ECHOES DWELL NEAR A WELL. Strange.

Upon receiving thorak's key, what does this open ?

A chest in Thorak's house with linking information on who poisoned Saskia.

I solved it by figuring out it was referring to things I already found. Like I noticed the stones already and the door.

The key opens a chest in Thorak's house.

c'mon, the poem was a nice touch. I got the well bit quite easily as i had done a relevent quest before, though i did scratch my head for some time to understand where to go from there but once i got it, it felt great to finally solve the puzzle.

I like the poem, it's just that there are areas that better fit the description in the poem compared to where you actually supposed to go.

I compeletely skipped the first verses of the poem and focused on the "guardian" verse, it was obviously the wooden statue near the quarry. After that, it was easy.

What wooden statue? I found a dead guy.

He's referring to the wooden statue at the crossroads before you get to the Quarry.

I knew to go straight to the Quarry when I read Geralt's journal about the signposts/rocks/whatever, because I'd already encountered those while previously exploring the area. Similarly, I went straight to Baltimore's workshop after that simply by guessing at the "drowned" clue and then searching in the appropriate area. You definitely don't have to follow all (or even most) of the clues.

The one that made me scratch was the line, "if you turn to the right you'll see someone's plight". At the time, I am obviously on top of the chest at the bottom of the quarry, so I turn right and I see nothing but quarry wall :)