what was Jesus's last name?

Surnames hadn't been invented at that time and place. If anything it would have been Bar Joseph (son of Joseph) as that was one method used to tell people with the same name apart.

Note that even in English, surnames have been used for less than 1000 years, and there are still countries in the world that don't use them. One example is Iceland, where people only have a first name. They make a surname by taking their father's name and adding -son or -dottir as appropriate. This is why their telephone books are in order of first names.

They didn't have last names, but in the Gospels, Jesus is identified as Jesus of Nazareth and Jesus son of Mary. (Christ is a title, not a name, if you were wondering.)

he would have been Jesus son of Joseph.

They did not have surnames in those days, but patronymics, such as bar Jusef (son of Joseph) were used, as were occupational and geographic titles.

they didn't have last names, back then. You were referred to as being of the city you were born or resided.

ie: Jesus of Nazareth.
Joseph of Aramthea (sp)

If anything, Bar Joseph

Only royalty or those who considered themselves to be above everyone else at the time had a last name.

Most people of that time where called something like Jesus Son of Joseph Or Jesus of Aramathea.

Last names really didn't start to be assigned to the average person until about 1200 AD. Around 1400 AD it became much more common for someone to have a last name, and if you notice most last names are associated with an occupation.

They didn't have last names in those days. Later on we developed last names like (Example) Nelson=Nels son, etc...that is how last names came about.

Either Ben Joseph or Bar Joseph.

Jesus has no last name because in the bible, mary and joseph is not recorded in the bible