While not strictly a bike, it is bike adjacent. I am trying to convert an old schwinn kids bike trailer into a dog trailer.

I am hoping to be able to grease the wheels. It looks like there is a ring I need to remove.

Hard to tell what's what, but I'd start by removing that snap ring so you can see if that metal collar is part of the wheel or not.

I suspect it may be a sealed bearing by the design, but I could be totally wrong on that too.

That is a dust cover. Behind that is a ball bearing assembly, which is probably not designed to be greased or serviced, only replaced.

The dust cover is usually rubber, and you can pick it off using a toothpick or small plastic prybar. Resist the urge to use anything metal on it unless absolutely necessary since this might damage whatever is left of the rubber.

Behind that you'll see one of two things:

A sealed bearing, which can't be greased or serviced...

...Or the cage of an open bearing which can be packed with grease.

When I say packed, I do mean packed. That's how open bearings work. Fill all of the available air space with grease, and if possible push out any of the old dirty grease in the process. You'll probably want a rubber glove. For particularly annoying to access recessed bearings I use a drugstore oral syringe, i.e. with a wide nozzle and no needle, via filling it using a popsicle stick as a spoon. I use the red Mobil 1 synthetic grease for this type of thing. And, indeed, practically everything else as well such as motorcycle hub bearings, swingarm linkages, etc.

If it's a sealed bearing that's trashed you'll have to replace it which is done via knocking it out from the other side and tapping the new one back in with a hammer, preferably after sticking it in your freezer for an hour or so to shrink it first.

i was searching for the name of that "snap ring" while you replied

i've finally found an image with it and it was labeled "Card-Spring-Retaining-Ring-Hole-Stopper-C-Shaped-Inner-Card-Hole-Stopper-Bearing-Positioning-Retaining-Ring-Washer" 😅

to op: be careful to choose a plastic friendly grease as i see too many plastic parts there

Haha, wow.

Hey bike company - that's a regular old snap ring!

Good point on plastic-safe lubes.

i was searching for the name of that “snap ring” while you replied

Circlip is the word you're after

Get the grease, slather

A sealed bearing, which can’t be greased or serviced

Yes they can. You can remove the seal, clean and re-grease it and put the seal back on. I've done this who knows how many times. It's not as easy/effective as with cup and cone bearings but it can definitely be done.

However, it's still recommended to remove it for easier cleaning so might as well replace while at it.

Yep. I'm using dentist's pick for removing the dust covers, it's a nice stiff and thin tool for this job