The Warrior Emblem, Avenger Emblem, and Destroyer Emblem absolutely stack (quote taken from the Destroyer Emblem wiki page): Note that the Destroyer Emblem, Avenger Emblem, and Warrior/Ranger/Sorcerer Emblem all can be equipped simultaneously for a stacking damage bonus.

Does celestial emblem stack with Avenger emblem?

Notes. The damage bonus stacks with all other emblems, including Sorcerer Emblem, Avenger Emblem and Destroyer Emblem. The pickup effect does not stack with the Celestial Magnet or the Celestial Cuffs.

Does sniper scope stack with Ranger emblem?

All emblems stack with all emblems, except with itself (since you can't wear 2 of the same accs).