Jeden Nachmittag trinke ich Kaffee auf dem Balkon.

In German, expressions of definite time without a preposition (like days, parts of day, dates) normally take the accusative.

• Jeden Nachmittag literally means “every afternoon.”
• No preposition is needed to mark when something happens; the accusative alone signals time.

Both indicate afternoons, but with a nuance:

• Jeden Nachmittag = “every single afternoon” (emphasizes repetition).
• Am Nachmittag = “in the afternoon” (more general, can refer to the afternoon of today, tomorrow, or afternoons in general without the explicit “every”).

Yes. Einen Kaffee makes it countable (“a coffee,” typically meaning one cup).

• Jeden Nachmittag trinke ich einen Kaffee → “Every afternoon I drink a (single) coffee.”
• Without the article, you refer to coffee in general, not a specific cup.

Certainly. The typical structure here is:

1. Time (Jeden Nachmittag)
2. Verb (trinke)
3. Subject (ich)
4. Direct object (Kaffee)
5. Place (auf dem Balkon)

German uses different prepositions depending on the idea of surface vs. interior:

• auf = on a surface or open space (e.g. balcony, roof, floor).
• in = inside an enclosed space (e.g. room, box).
  A balcony is considered an open, accessible platform, so we use auf.

The preposition auf can take either dative or accusative, depending on motion vs. location:

• Dative after auf = no movement, static location (“on the balcony”).
• Accusative after auf = movement toward that surface (“onto the balcony”).
  Since the action is happening while sitting on the balcony (no movement toward it), we use the dative dem.