Hi, I am just beginning and have a very basic understanding of music. I have a C whistle and have read that I can simply use the same fingering as on a D whistle. This seems to work fine following the fingering charts for a D whistle with various pieces. I suppose everything is relative, except when I attempt a C natural (leaving all holes uncovered) it just doesn’t work - I would like to know what fingering I should be doing - hope this is clear 
Leaving all holes uncovered on a C whistle will produce a note of concert B natural. Is that what you were after?
a C natural (leaving all holes uncovered)
All holes uncovered is (on a D whistle) Csharp.
All holes uncovered is C#, as mentioned above. For C natural (in D whistle terms) you could use OXX-OOO fingering (covering only the second and third holes from the top). There are a few other ways of cross fingering that note, but that is the most common. You can also cover [roughly] half of the top hole to get a C natural.
As I feared I have not explained my position very well, I have a C whistle (I have a D on order) so I am learning what I can in the meantime. When following letter notes written for a D whistle, as I have read is workable, such as: D G A B c B A B A G E G B A for example, all works well using D fingering on my C whistle, except for the C note (open holes) which clearly doesn’t follow the pattern it sounds quite off. Also thank you for the responses so far, I appreciate the assistance.
I can’t tell for sure, but that looks like the note you are after is Cnat (in D whistle fingering) as the sequence of notes you’ve given looks like a piece in G. As stated bi Sirchronique above, the note Cnat is not fingered with all fingers off, but rather the second and third finger of the top hand cover their respective holes, ie the second and third holes from the top are covered, usually represented like this:
OXX OOO
Does that help?
One other thing to consider: Very few whistle players (and probably no traditional players) learn the names of the notes on anything other than a D whistle. So when switching to another whistle, one just plays it as if it were a D whistle. Even if I’m looking at sheet music, if I have a C whistle in hand, I’ll still use sheet music with one or two sharps–music for a D whistle. If you hand me music written in C, I have to do mental gymnastics to make it work on the whistle.
In other words, until (or even after) your D whistle arrives, pretend your C whistle is a D whistle.
That
should more or less sort you out. Second octave Cnat best half holed though.
At the top of the second octave, OXOXXX often works better for C-nat and OXXOOO better for high D.
I agree with Ben … That tune’s in G major, so you’ll want to play C-nat. What is the tune BTW?
Great, thank you all for your time and assistance that’s me sorted for the moment till the next problem 
the example I used was from Buachaill on Eirne or Come by the Hills.
Ah yes. Definitely in G then, with C naturals ( OXX OOO ) rather than C sharps.
PM me for some help.
Hi, if you would like to play C natural on a C whistle the fingering is OXXXXX .
I think I had this conversation the other day …I said as long as your piece of music is always written (or transposed into) the key of D or G the fingering will always be the same …then its just a matter of changing your whistle to the key you would like the tune to come out in …I think …(my head hurts again ) 
John