"Vala kostōbe āeksio urnes."

Translation: The man sees the powerful lord.

[Kaceyon]

How am I supposed to know which noun that the adjective is attached to?

[xPsGoDWh]

The ending gives it away. If it modified "vala" it would have the lunar nominative singular ending -a, but since it modifies "āeksio", it has the lunar accusative singular ending -e.