Shortened version of "knackered". When you are so knackered you don't even have the strength to say "knackered" and can only go as far as "knacked".
The wife made me work out this morning. I'm totally knacked.
1. To be scolded, told off(see bollocking).
2. To be in pain.
1. I forgot my homework so my teacher knacked me.
2. I hit my hand off the wall and it knacked(If it's hurting at the time you say it is "knacks").