Josper is not a Spanish name, that is sure.
It seems more like a variant of the Dutch
Jasper, Caspar, or like a misspelling of
Jospert, variant of Jaspert/Jasbert, old French/Occitan/Catalan forms of the Germanic name
Gautberht, from
gaut, "goth", and
berht, "bright".
Lumia
http://onomastica.mailcatala.com