The answer to your question would be that the phrases from the passage that are oxymorons are the following ones: "happy dagger" and "timeless end".
An oxymoron is a figure of speech in which apparently contradictory ideas appear together. As a dagger is a weapon, it is wear that it appears next to a positive adjective such as "happy". As regards "timeless end", it can be said that the end of something represents a conclusion, it has an "end point", so it is contradictory to say that the end is "timeless".
The dictionary explains the exact meaning of the word and its different interpretations. The thesaurus gives you different words with the same or similar meaning.
