Did you have Nicholas Bonnitcha in your tree before you took a DNA test?
If you think he might be a DNA connection, have you built up a tree for him? You might need to consider the female line as well, eg his wife, as you may connect that way.
You mention naturalisation(?) - depending on records, searching in foreign lands could present you with difficulties.
Do any of your matches have trees you could look at? Have you made contact with any of them?
Added: I presume you have already seen this:
https://www.tribalpages.com/tribe/browse?userid=bonnitchaUnfortunately not much seems to be known about his origins.
Of course, your common ancestor could be earlier than Nicholas, but it might be easier to look into Euphemia’s family first?
What does his naturalisation certificate say about his place of birth? This should be information provided by him so should be fairly accuarate. I can’t remember what is on Tassie certificates, but do either of his marriage certificates name his parents?
Reason I ask is that the dna connection may be further back. Also consider siblings as descent may have come through one of them.