get it aspirated COULD be cancer
Gosh, have no idea but that looks pretty nasty. The fact that it smells is probably infection and really should be checked by a vet. Don't use any more hydrogen peroxide as it can actually damage the cells. Use just plain warm water or a mild anti-bacterial soap then rinse well and dry it well. If working near the ear, put a cotton ball inside the ear to keep it dry then remove it when you are done. If you have one of those rubber bulb syringes (like you use for your own ears or for babies) use that to flush the area. Even a turkey baster would work but don't hit it with a lot of pressure. Make sure whatever you are using, like scissors, etc are cleaned before and after. Hate to say it, but this probably should get checked before it gets worse and ends up costing twice as much to treat.
Sorry about typos. Im on my phone so I could post the picture.