gus i can not understand something what is spike's surename?

Spike's surname is never revealed in the series but if you read the comics (not seasons 6/8 but the others that fall between episodes of the series) it is revealed the his human name is William Pratt in Spike: Asylum by Lynch. It is not said but in that comic his is issued a container of blood (it's a baddie rehab) and the container is labeled William 'Spike' Pratt along with his year of siring. His birthday is not revealed though.

This is one of my favorite comics, truly recommend you picking up both this and Spike: Shadow Puppets as they read as a series

William Pratt