I can't see, but are there any splines near the axle? That two hole appears to be the lockring of the ratchet mechanism, and that two grooves appear to be from the freewheel body to hold it while removing the cogs one by one. But remove the axle and look/touch the inside of the axle hole, is it splined?

I have a russian hub with cogs, that are not removable (the cogs one by one can be unthreaded like this freewheel also, and any other, also i can remove the whole cassete by unmounting the oneway ratchet mechanism, so I'd have to demount to the pawls/those 100 little balls/ springs etc.) The fixed part of the pawl holders is cast with the hub so not removable and not interchangeable with anything - this my case, but can be in your case too, if it does not have splines inside it, and cannot see something else beside the two-hole cap (that holds the oneway ratchet mechanism), then it may be cast from the same piece.

If this is the case, you might remove the two-hole cap, and check the ratchet mechanism (pawls, fractured balls, dent raceways, pitted raceways, detensioned or broken springs, etc) to see if it worth saving the hub
If it's all in good condition, you might check the cogs if they're good. The cogs can be removed one by one, and replaced from another freewheel. But that ratchet mechanism will be stuck forever (it's cast with the hub)

But i hope it's removable and not one-piece because it's an ugly thing to change the hub (despoke-respoke-trueing, different spoke if the flanges of the hubs are not the same. etc)