cut on ear

I'd go by whether or not it's healing well -- if it is I'd just use a wet washcloth with mild soap on it and keep it clean.  don't scrub - just cleanse it.  As long as it's healing well leave it alone.  Sometimes less is more with stuff like that.  But if it looks red and ugly, have a vet look at it.

This happens to me all the time. Get in line at the guilt handout place. Since my dogs work out in brush and stuff way away from me, alll the time, and since they tend to hurt themselves and not even react, being so wrapped up in their work, they can get a small nick and I won't notice until a couple days later when I am playing with their coat or grooming or whatever.

You didn't notice it probably because it bled a bit (ears bleed freely even with tiny wounds) and then the coat covered it. When the scab falls off, typically the hair around that place will be pulled away. It's OK by then - ideally you want to clean it at the time it happens and cut back the hair, but small superficial wounds don't usually get infected easily. It's the puncture wounds that get nasty, or deep cuts. I put a little tea tree oil on it so the dog won't lick it, to ensure fast hair regrowth. Nature takes care of the rest.

this is where an E-collar might be used if the dog is scratching at it...otherwise time will heal all