You have to clean the engine bay first
When troubleshooting for the source of an oil look you first have to completely clean off all of the old oil, dirt and built up grime.
You can get a citrus based cleaner for oil at an auto parts store. Typically you will heat the engine up enough to make it warm but not hot enough that if you sprayed something on the engine that it would evaporate quickly. Citrus based cleaners are water soluble so you can hose them off. You may want to brush around the bay, especially underneath the motor where most of the gritty grime will be builtup.
Once clean, do the following
Turn the car on, get it good and hot and ensure that all the water is evaporated. You may want to drive it a short distance but not so far that you will dirty it up again.
Place a large piece of cardboard under the engine. See where drips might be forming and dropping onto the cardboard. When you have a drip you will want to chase it up to it's source. The oil might run along a wire and drip. It may leak down the side of your engine, drop onto a suspension arm, run down it and then finally drop onto the ground. The source can be difficult to find.
Check areas where two engine surfaces meet. If you have a failing gasket it will be something like this. A valve cover, an oil pan, something like that.
Check oil lines - You may have an oil line coming loose that is dripping. Take into account the air movement from a fan or driving down the road at a high rate of speed and oil can get sprayed everywhere. Which is why it's important to clean EVERYTHING before you start you hunt.
You can also try throwing talcum/baby powder all over the place and blowing it off with a leaf blower and see where it has built up. It's a painful way to do it but I've found the leak source doing this before so sometimes it's a good method depending on where the leak is.