To Get 110% completion of every stage you need to the fallowing in each stage.
1-Complete the stage at Paladin difficulty (highest difficulty that unlock only after beating the game once at any other difficulty)
2- Find all items in the stage (life,shadow,light gem and Brotherhood arks)
3- Complete the Trial of the stage.
When all this is done the stage as the 110% completion mark.
Note: All of this can be done on multiple playtrough if needed. In other word you do not have to collect everything and do the trial at paladin to obtain 110%. You could collect everything at esquire, beat the trial at warrior and beat the stage at paladin and get the 110% since the game track your progression each time you do them.