That’s your brake vacuum pump and that’s a metal plug on top of it. It’s not leaking from there unless the middle of your plug has a hole - doubt it. What you’re seeing is residual oil from elsewhere.
Clean all around that area and check your oil level. If OK, very briefly run the engine to look for the leak. It could be coming from where the pump mates to the engine. There are two o-rings inside the pump that can fail, although I’ve never seen oil leaking on top of it - it usually drips under the pump and collects on top of the transmission. From your photo it appears that oil is spraying out as opposed to dripping.
Edit: Also check the power steering pump and its level which is just in front of it (where you add ps fluid). There are pressure hoses connected to it and one could be leaking under pressure and spraying fluid on grime on the engine making it look like an oil leak. The ps fluid has a greenish-brown tint to it.