Since alkene consists of carbon carbon double bond,and is made up of sigma bond and pi bond.double bond itself is 4 electrons.remember C has 4 outer electrons,2 electrons are shared with hydrogen(covalent bond) so it is left with 2 electrons to share with another C which is the same.pi bond is a part of C=C,thus i believe it has 2 electrons since another 2 electrons is in sigma bond.
I think.correct me if i am wrong.