I think I can make out these letters obv:
10:00 to 11:30 annelet I O (the gothic O that is pinched)
4:30 to 6:00 E S annelet
6:00 to 9:00 DE[I?] GR[A?]
I'm not seeing an O at all, unless the gothic O looks really
unlike a regular O. Which I don't think is the case.
(Now that I think of it, there's an O in MON[ETA] on the reverse, which has approximately the shape I expected.)
Here's what I see (relative to the rotated image):
3:00 to 6:00 N? N E S annelet* (faint, but relatively clear, especially the second N at 4:00)
6:00 to 7:30 D? I? ? annelet? (can't make much sense of those letters)
7:30 to 10:30 G R ? annelet (this much is clear, assuming that's what a G looks like)
10:30 to 12:00 D? R? X? (only the upper left line of the third letter is visible, but it fits an X and not much else)
The section from 12:00 to 3:00 is flat and/or clipped, and would not yield any more letters.
This is consistent with a legend reading [IOHA]NNES:DEI:GRA: and either DVX or REX; the latter fits the letters I see slightly better.
Brittany did have several 14th century rulers named John/Jean, so in principle it could be one of their coins.
On a quick search I couldn't find any
example (either French or Breton) that had the two-line legend in the circle placed so low, and/or that had a [name]:DEI:GRA:[title] legend.
Come to think of it, with some squinting we could probably read [IOHA]NNES:###:FRA:REX, which I think
might fit the catalogued legends slightly
better, but I can't figure out what the ### could be.
I'm reading BI[S?], which makes no sense, I think? The first letter could also be an E or, with some squinting, a D, and the third letter is just a blob at 7:15.
I think I can
read DEI if I try, which would fit if the G actually is a G (which it probably is, now that I think of it), but we'd have to assume some damage at 7:00ish to make the E look like an I.
Maybe I just misinterpreted the letter spacing and the D starts half a letter earlier (immediately after the annulet, nearly touching it).
Then I can kind of see EI in the next two letters... on second thought, it would require a rounded E, while all the other E examples on this coin - in [IOHA]NNES, in [DV]PLEX, the visible left part in MON[ETA], and in REX if that's what it is - are plainly rectangular (plus serifs). So that doesn't work either.
*) I'm assuming that "annelet" refers to the two-ring colon thingy; I don't think "annelet" is the correct term for it, but I couldn't find the right word on Google, so I'll just keep using this one for now
[EDIT: apparently this forum's editor joins together my multiple question marks; I exchanged them for other symbols in the one place where the number was important, and I guess I'll just have to live with being less clear everywhere else.]