Open your Adobe After Effects project file.
Make your workspace layout as such: Go to Window > Workspace > Animation. The layers you are looking for will be in your timeline, which is now centered at the bottom of your workspace.
Identify the layer you need to make visible. Even if your layer is invisible in your canvas, it will appear in your timeline. To the left of the timeline in the same row, each layer has a name. When you have identified the layer you would like to make visible, click it so that it becomes highlighted and you don't lose it.
Move your mouse to the left of your selected layer while staying in the same row. The left-most column in the timeline panel of your workspace is visibility. This is signified by an open eye icon at the top of the column. If your layer is invisible, there is an empty box in this column. Click inside the empty box. The open eye icon will appear inside the box, and your layer will appear in your canvas.