stick an layer positon on another left up corner of a square layer in After Effects
The position of any point on a layer in terms of its location in the composition frame is given by the layer space transform function toComp(). Since the top left of a layer is the origin in After Effects, from the point of view of the solid its top left is going to be [0, 0]. So we find the position of the point [0, 0] on the layer in terms of the comp thus:

thisComp.layer('&lt;name of the solid&gt;').toComp([0,0])


Apply that to the position property of the layer you want to stick to the solid.