What game is it where a dog herds sheep? - briefly
The game you're referring to is "Sheep Dog and Sheep".
What game is it where a dog herds sheep? - in detail
The game you're referring to is likely "Puzzle Bobble" or one of its variants, such as "Bust-a-Move." In these games, players control a character that shoots colored bubbles at the top of the screen. The objective is to match three or more bubbles of the same color to make them disappear. Over time, various themes and characters were introduced into the game, including one where a dog herds sheep. This specific version adds a humorous and whimsical touch to the classic puzzle-solving gameplay, making it even more engaging and entertaining for players.