why is there no word for "of"?
German doesn't do that. There is a word for it, but all the phrases like this that have of in English just have two nouns together in the same case in German. Cup of coffee, bowl of soup, glass of wine, etc.
why is "a wine glass" not accepted
Because we are yet to see a glass made of wine, and not just containing it :)
Why without umlaut? I thought it was - Das Gläs = the glass...
“the glass” = ‘das Glas’; “the glasses” = ‘die Gläser’
Why not use Genitiv here?
If this translates as “a glass of wine” how do we say “a wine glass”?
It makes sense. Thank you.