Hello, i don't remember about an official tab with them , but you can see the items of others player's hero , and add to that the percentage from using oil which is visible just for the player itself . ( the max percentage by oil is 15% ... )

From what i know , (we have 4 slots at the left and 4 at the right )  the 1st slot max 32,5 % , 2nd slot  40 %, 3rd slot 47,5 % , 4th slot 40 % .

I wish you a great day and enjoy the game !

Yep, the max bonus you can get to either offense or defense (by equiping 2 rings of the same type) is 192.5%.