There are a total of 11 workbenches in the game.
"The Outskirts": At the museum's basement, after escaping the infected through a garage door.
"Bill's Town": At the church's basement.
"Pittsburgh": There are three locations. The first one is located after defeating the hunters at the start of the chapter, past their sleeping quarters in a room, before dropping down into the street. The second one is in an office right before the kitchen in the hotel, after Joel escapes the basement. The third one is in a building, on the second floor by going through a garage door.
"The Suburbs": Inside the open garage of one of the houses.
"Tommy's Dam": In the dam control room, on the left side. Gets destroyed when bandits attack the dam.
"The University": There are two locations. The first one is in a room where Joel obtains the flamethrower. The second one is in a science lab, on the left side where Joel first entered the building.
"Bus Depot": There are two locations. The first one is in a tent, right before Joel enters the bus. The second one is in the hospital's ventilation system, in the first room, where Ellie lets Joel in.
Source:
https://thelastofus.fandom.com/wiki/Workbench#LocationsIf you'd like a more comprehensive guide, you can check out PowerPyx on YouTube