However, the skill description of Horn of Gandarr only shows 1051 elemental damage without any burn, frostburn and electrocute damage. (Sorry that I cannot upload more than 1 screenshot as I am new to this forum)
Is it just display issue or the skill modifier does not added as expected?
sadly the ui isnt really reactive like that - apart from direct conversion on a main skill. put horn on left/right mouse button and check the second tab of you character sheet, you will see the damage over time component is there.