can we also say:
"jeden Freitag trinken wir wein" ?
I mean, if we do not use the word "an" at the begining, would this be correct?
I'm not so sure. At the very least Freitag would have to be dative because we now have 3 nouns without prepositions, wir is nominative and Wein is accusative and freitag is clearly not Genitive so it must be dative.
It is because in plain sentences, a verb has to occupy the second place from the beginning: - “Wir trinken Wein.” 1st place: who, 2nd place: verb, 3rd place: the rest - “An jedem Freitag trinken wir Wein.” 1st place: when, 2nd place: verb, 3rd+ place: the rest.
Just as a sidenote, in more elaborate sentences, such as those with two verbs, the second verb has to be at the end of the sentence.
Is An Jeden correct? Duolingo says no. I'd like to know why? Since jeden also means every or each.
It isn’t correct. The prepositions require specific cases to be used. “An” requires a dative, which for “jeder” is “jedem.” “Jeden” would be an accusative which is not appropriate after “an.”