ok, what does happen when I play DCC and I find only the Great Book of Grudges? Can I put it into play aggregated to a unit (for examples DCC itself)? Or I can't do that?

I think I can becuse DCC text doesn't specify which type of support you can play. the DCC only check for the cost.

Maybe it's a stupid question. but I am a bit confused

Yes, if it's a support and the cost for you is 2 or less, you can put it into play.

If you put a card into play and it contains a direction on it those directions must be followed unless the effect which puts it into play gives some other direction. In this case if it says attach to a unit, then that is something that must be done.