How much of the ice on Earth is floating (such as icebergs, or perhaps all the ice up at the North Pole)?
A first-order estimate is about 5%.
This is a trickier question than it first appears because of ice shelves. Quoting from Kusky (2014):
Ice shelves form where ice sheets move over ocean waters and form a thick sheet of ice floating on the water and attached to the land on one, two, or three sides. Their seaward sides are typically marked by a steep cliff up to 1500 ft (500 m) high, where many glaciers calve off from forming icebergs.
So they are floating, and they can be up to 2000 m thick, according to antacticglaciers.org. So they definitely make a substantial contribution to the world's sea ice fraction.
Continuing with Kusky:
Ice shelves are found in Antarctica, Greenland, and along the polar seacoasts of the Canadian Arctic Islands. The largest ice shelves are contained in Antarctica, which contains 91% of the world's glacial ice, around 7% of which is contained in ice shelves. These ice shelves cover 50% of the coast of Antarctica, forming an area 1/10th the size of the continent.
If you don't take ice shelves into account, and only think about pack ice, you end up with about 0%, because pack ice is generally thinner than about 4 m, and so makes up a tiny fraction of global ice volume, in spite of its extensive area.
But if you do account for ice shelves, especially the southern ones, the answer must be much greater. I have not done the research to find the numbers, but the text I quoted suggests something less than 7%, so I'm going with 5% as a first-order, round-number guess.
Kusky, T M (2014), Encyclopedia of Earth Science, New York Academy of Sciences, 529 pp. In Google Books.
The Antarctic land ice averages a little over 1.8 kilometres thick. Greenland ice averages a bit more than 2 kilometres thick. The circum-Antarctic ice thickness averages only between 1 and 2 metres in thickness, whilst the Arctic (all sea ice) varies between 1 and 5 metres thick - it was >6 metres thick but global warming has been thinning the ice in recent decades.
At its maximum winter extents the sea ice is comparable in area to the continental ice, so the fraction of global floating ice is about 0.1%. If you need a more accurate answer then I suggest you trawl the internet for areal extents, and do a seasonal mass balance. Obviously, it will vary according to which hemispheric winter you choose. I suggest 'Arctic Sea Ice News' https://nsidc.org/arcticseaicenews/ as a good starting point.