Thank you John.
My Danckert / Dankert is a very long shot, although so far as I can see there were not many of them.
My GG Grandfather Howard Gillman Daunt born 1811 ish was the son of John Daunt, a shoemaker. I've found a John Daunt shoemaker in Cork in 1810 in Holden's Directory.
I also found on Family search a marriage record between a John Daunt and Harriet Danckert in 1797 in Rathcooney Cork.
That's it! As you see it's a bit desperate. On the other hand that's the only likely John Daunt too, and HG Daunt named his third daugther (my G Grandmother) Harriet.
A kind researcher discovered some Danckert obituaries on the following site:http://www.irelandoldnews.com/obits/
Any further clues very welcome here too.