Hypothetical here ... if a dog is owned (on the reg cert) by two people, say husband and wife, and one of those two has an affix, can the dog be given that affix?

The affix & owners has to be in the same name. Although the dog could be put into mr X(affix holder) affix added then transfered into Mr & Mrs x to get the affix on.
I have a feeling it may be different if there could be seperate or joint interests on the affix??

My youngest boy is owned by myself and husband and daughter - affix is in mine and husbands.  Basically he was transferred to mine and husband, affix added then daughter added via transfer.  Also know a friend did similar with her sons dog to get her affix on

No, you would have to change the ownership into the name of the person who has the affix, add it and then change it back again, or add the other person to the affix (vary it, which will cost).

I thought as much. Thanks!

That's interesting.  One of my boys was sired by a co-owned dog.  I expected the person who bred him to have her affix.  But the dog, who got his JW, just had his name - we'll say Wet and Windy, with no affix or suffix.

I co own a bitch which I bred with a friend, as we don't share an affix we have registered a loan of breeding bitch with KC, for duration her breeding years, so any pups will be registed with my affix. Without this or transfer of bitch back into my sole ownership no affix ( hers or mine ) could be used on the pups.