The Destined Heroes (and subsequently Lost in the Light / Found in the Dark) quests are only given once per account. You've already completed it on a character, so your alternate characters (ie Titan) will receive its missing Grenade/Super/Melee/Aspects from doing the 6 adventures located near Ghost in the Pale Heart. Two adventures are right next to Ghost, two are on the far left stairs that leads down to where the Speaker used to be located, and the other 2 are on the right side stairs. The adventures and their specific rewards for your Titan are as follows: The Hollow Part 1 - Consecration The Hollow Part 2 - Hammer of Sol Queens Part 1 - Suppressor Grenade Queens Part 2 - Shiver Strike Home Part 1 - Drengr's Lash Home Part 2 - Glacial Quake