Drawing Entities on non-current levels faintly
On the layout, select the Plan View port. Use the visibility switches to turn on the levels you want to see.
On the plan view port Properties, change the Draw Entities on Non-current level faintly from No to Yes, and then choose what level you want to be the Current level.
Entities on the current level will be drawn full color, those on other levels will be drawn faintly.