Does anybody know where this sticker is used or the set number it's used in?
This piece is 42023pb005R - Slope, Curved 6 x 1 Inverted with Orange and Yellow Marbled Flames and 'G' Pattern Model Right Side (Sticker) - Set 8897, which is used in only 1 set: 8897 - Jagged Jaws Reef.
But once more, please look at the Catalog Search function in BrickLink and spend some time learning it - this is the third consecutive "What is this piece" question for pieces that are fairly trivial to find. Bricks with a curved end are called "Slope" and are a common type (other common types are "Plate", "Brick", "Tile", "Minifig", "Wheel" etc.). You can also use the search bar at the top of the BrickLink screen, just make sure you switch the Search Scope field to "Catalog Item".