In Cockney rhyming slang, "knickers" is used to refer to a watch. This comes from the phrase "knickers" rhyming with "clockers", which in turn is slang for a watch.
So, instead of saying "watch", a Cockney speaker might say "Have a look at your knickers" or "What time is it on your knickers?".
Let me know if you'd like to know more about Cockney rhyming slang!