TL;DR: There is some chance that the drink, if it existed, had a taste combining coconut and chocolate. It is far from clear though, since that usage might be newer.
I agree with Thomas Carroll's suggestion that we need to consider phonetically similar variants. Polish has the rare feature of transcribing all foreign words, even the ones written in its own Latin alphabet, into their phonetic equivalent. Also, considering the geopolitical setting, an exotic drink might have entered the area from Russia, and the name would have been transcribed from whatever a Russian merchant called it (in writing or orally).
This gives us three rather likely potential replacements for "kakawelo". The first is w -> b. This is commonly done at least in Russian (compare e.g. Вифлеем, Vifleem, for Bethlehem). Then there is a -> o, because in Russian, an unstressed o sounds like a. Third, k -> c is also a likely pair, since c in Polish is pronounced close to the zz in pizza. Also, the "l" could be doubled or singular.
With these replacements, I considered names matching
coc[oa]bell?[oa]. I actually also tried replacing the first "o" by an "a", but not only is it unlikely (it is stressed); the closest hits were misspellings of the cascabel pepper or of the plant Cascabela Thevetia, which happens to be poisonous.
Luckily, the other searches led to several unrelated hits for "cocobello": different Swiss chocolatiers are offering a chocolate candy under this name, always consisting of a coconut gianduja center with chocolate glaze. There was also coconut-chocolate spread by a UK manufacturer called "cocobella". This is what I consider to be the likeliest taste direction of the drink, since it is the only use which is not bound to a single (modern) brand.
You must also consider that these word variations sound nice, and seem to have been re-invented several times. So, there is also a chance that the antique usage did not survive (it might also have been a brand rather than a generic name) and that the Swiss chocolates are newer. Or, it could even be that the drink never existed and was invented by the author to imply fanciness.