Jeg kan ikke vente lenger.

After Norwegian modal verbs you use the bare infinitive (without å). The common modals are: kan, skal, vil, må, bør, tør.

• Correct: Jeg kan vente.
• Incorrect: Jeg kan å vente. By contrast, with non-modals you normally include å:
• Jeg liker å vente.
• Jeg prøver å vente.

In a main clause, ikke comes after the finite verb. With a modal + infinitive, it sits between them:

• Jeg kan ikke vente lenger. Without a modal, it comes after the finite main verb:
• Jeg venter ikke lenger. In subordinate clauses, ikke comes before the finite verb:
• fordi jeg ikke kan vente lenger
• at jeg ikke venter lenger

They’re close, but not identical.

• Jeg kan ikke vente lenger = I can’t wait any longer (I’m unable/unwilling to continue waiting).
• Jeg venter ikke lenger = I’m not waiting any longer / I no longer wait (a simple statement of what I’m doing).

Both exist in Bokmål. A practical rule of thumb:

• Use lenger in the set phrase ikke lenger and as an adverb about time: kan ikke vente lenger.
• Use lengre more often before nouns (adjective): en lengre pause, lengre tid (“a longer time”). For distance, both appear, but lenger is very common as an adverb: Går du lenger?

Context decides. kan can mean:

• ability: I’m not able to wait any longer.
• permission: I’m not allowed to wait any longer (less likely here without context). You can be clearer with other verbs:
• vil ikke (won’t), klarer ikke (can’t manage), gidder ikke (can’t be bothered), får ikke lov til å (am not allowed to).

Use a preposition if you specify what you’re waiting for or how:

• vente på
  • something/someone: Jeg kan ikke vente på bussen lenger.
• vente med å
  • infinitive (postpone): Jeg kan ikke vente med å spise.
• vente til (until): Jeg kan ikke vente til i morgen. Without an object/complement, vente stands alone: Jeg kan ikke vente lenger.

Norwegian main clauses keep the finite verb in second position. If you front something, kan still comes second:

• Nå kan jeg ikke vente lenger.
• Derfor kan jeg ikke vente lenger. Subject moves after the finite verb when something else is first.

Approximate guide (Eastern Norwegian):

• Jeg ≈ “yai”
• kan ≈ “kahn” (short a)
• ikke ≈ “IK-keh”
• vente ≈ “VEN-teh”
• lenger ≈ “LEHNG-er” (ng as in “sing”) In casual speech, many compress kan ikke to something like “kanke” in pronunciation. Keep the full spelling in standard writing.

It can be, but Norwegians often prefer an explicit “looking forward” phrase:

• Jeg gleder meg! (I’m excited/I’m looking forward to it.)
• Jeg kan nesten ikke vente! adds the excited tone (“I can hardly wait!”).

Yes:

• Ikke vent lenger! (Don’t wait any longer!)
• Positive imperative: Vent ikke lenger! (more formal/literary)