Pensak looks a lot like Penzag which according to the dictionary Jewish Family Names and Their Origins is a variant of Penzig, the origin being the placename Penzig in Poland. The surname Pensak was also written Penzik in the same family as you can see at
http://awt.ancestry.com/cgi-bin/igm.cgi?op=GET&db=jaelsne&id=I170. You'll also find the form Penzak at
http://tr.im/sX1J.