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this lot. I suggest you read through some of those first.
I've only got the recipe out of "First Steps" which calls for 1 level tbsp of instant coffee, 1kg of sugar and 1 tbsp of citric acid, plus yeast and nutrient. I have made that, only once, and it was vile, but that was a very long time ago when I was still a teenager and probably didn't have a clue what I was doing.
If you wanted 20% abv that would need 1.75kg of sugar and a yeast which could tolerate that sort of alcohol level.
However, there's sod all in that recipe to give the wine any body so it's probably best left light.
You need a big wine to carry off that sort of alcohol level. It is possible, things like wheat & raisin or parsnip sherry can be pushed to the limit. However, the stronger you make it, the longer it needs to mature, and I'm talking 2-5 years for the ones I just mentioned.