I am doing the Watchtower quest.  I have been following the Wiki guide https://oldschool.runescape.wiki/w/Watchtower. When I come to the broken bridge right before the guards who give you the Skavid map, it gives me the response "I can't reach that" when I choose option  "Jump-Over" by clicking on side of the gap for a red X option.  I retraced my steps  and even spoke with the WIzard in the tower.  But can't progress beyond getting the Skavid Map,  Please help? 

I could be wrong, but it sounds like your agility isn't high enough.  According to the Tip.it guide https://www.tip.it/runescape/quests/view/64-watchtower, you need 25 agility.