Apparently, it's a long-standing tradition handed down orally that the Roman soldier who raped Mary was called Panderik. So I've been told. Caveat Emptor.
Yoshke is a diminutive of J.
For an online source see the bottom of this page which claims:
Yoshke Panderik (יאָשקע פּאַנדריק) or Yoshke Pandre (יאָשקע פּאַנדרע). A book called "Toldot Yeshua" claimed that his father was actually a Roman soldier named "Pandeira," whose identity was hidden by Mary. See also: http://forward.com/culture/160737/yoshke-of-nazareth/
The link quoted has other ideas. Yoshke is'nis not really diminutive but nomatricon (abbreviation) of Yimakh shemo יִמַּח יִמַּח שְׁמוֹ "May his name be obliterated" is a curse the name of particular enemies of the Jewish people. Note that the full phrase ימח שמו וזכרו has the abbreviation ישו which is also the transliteration of the name used for that person.