Simply put, a kenning is a way of describing something without actually mentioning what it is. A metaphor, if you like.
For instance,
Slaughter dew = Blood
Sleep with the sword = Death
Swan of blood = A Raven
Therefore your answer must be A or B
Although I'm not completely certain, I would guess that King hrothgar is a 'Shielder of shield bearers', as he is a king.
Sorry I couldn't be of more help.
Good luck.
