The pronouns in this song are interesting. It would make the most sense as How should I MY true love know? But it’s not that. It’s how should I know YOUR true love know? In a way – if this is directed at one’s lover – it’s asking, “How am I to recognize myself? How do I know which part of me, which identity, is your true love?”
The usual way is to wonder if one’s love is a true love. It’s “How will I know?” or “It’s in his kiss.” Or any other multitude of popular songs that ask the question of whether a love is true or not. THIS question is much more interesting. Which self am I? Which one of me is your true love?
In a woman who’s had her whole sense of identity shaken, this becomes an even MORE interesting question.