It's pronounced like 'dhunnakha" (dh like th in there).
The Irish equivalent of Denis is Donnchadh; Scottish Gaelic: ?
Donnchadh
In Irish it's "Donnchadh"Although they are not connected, the old Irish name Donnchadh is considered "equivalent' to Denis. It Scotland it is anglicized as 'Duncan'.
Roughly dhunn-a-ha (dh = th in then).
In Irish it would look like "Donnchadh Seán".
Donnchadh of Argyll was born in 1175.
Donnchadh of Argyll died in 1244.
Donnchadh mac Urchadh died in 959.
Donnchadh Ó Hámsaigh was born in 1695.
Donnchadh Ó Hámsaigh died in 1806.
Donnchadh de Strathearn died in 1355.
It would be the same. Names are not 'translated' as such, many have 'equivalents' or 'substitutions' commonly accepted such as Seán for John or Donnchadh for Dennis in Irish.