The english term "mocha" refers to a beverage made from coffe, cocoa (typically as sirup) and milk. There is no real equivalent in German. Most likely it will be refered to as "Mocha", with the english spelling. Kaffeverband suggests Caffè Mocha, so that's probably the best translation (although it makes it sound much more italian than it actually is, according to en.wikipedia.org it is an american invention).
In Germany, "Mokka" is usually understood to be turkish coffee, a special way of preparing coffee. It is also used in a lot of brands etc for things containing coffee and cocoa. So technically the other leo entry "mocha" - "Mokka-" (in German with dash at the end, indicating the use as part of a word) is correct, although it will confuse English speakers who want to order a "mocha" in Germany, or Germans who want to know what a mocha actually is (the latter was the case with me!). Therefore the entries for "cafe mocha" and "Turkish coffe" really need to be added.
The expression "mocha coffee" is used in english to describe the type of coffee from Mocha, Yemen/Mokka, Jemen. This is the original meaning of mocha, but nowadays a "mocha" is the drink (made from any coffee) you can get from one of the many coffee shops. I don't think there is a German term, so the best way is just to descibe it what it is - coffee from a particular place in Yemen.
Having written so much about coffee, I think I'll need to get one just now ;-)