View house drawings
Look at the drawings of the house, those thick black lines are the signs of the load-bearing wall!
Knock on the wall and listen to the sound.
It's also a good idea to knock on the wall and listen to the sound. If there is a clear echo when knocking at the door, it is mostly a light wall rather than a load-bearing wall!
Observe wall thickness
Observe the thickness of the wall. Usually 150mm thick partition walls are mostly non-bearing walls, such as toilets and kitchens.
Observation wall brick
Observing wall tiles is also a simple method. Standard brick walls are usually load-bearing walls, and aerated bricks are non-load-bearing walls!