Jackie

I'm glad that you mentioned "knock on wood", I'd always half listened to the song, wondering what it meant. The usual expression here in the UK is "touch wood". When children use this expression the joke is to touch a friend's head (implying that it is wooden) - do you have the same joke?

More knocks:
When shops have a sale they often talk about "knockdown prices".
I think that the impregnate version of "knock up" became known in the UK during the war, when GI's were most amused by being "knocked up" in the morning.
To knock something up would be more likely here (I think) that knock something together (meaning a rough version or "mock up") although the latter may be coming into use to avoid the obvious innuendo.
I used to live near a place called Knockin in Shropshire. The local shop proudly displays its name above the door - "The Knockin Shop".