Howbeit (αλλα). Clearly adversative here.

This man (τουτον). Possibly contemptuous use of ουτος as may be true in John 7:25; John 7:26.

Whence he is (ποθεν εστιν). The Galilean Jews knew the family of Jesus (John 6:42), but they knew Jesus only as from Nazareth, not as born in Bethlehem (verse John 7:42).

When the Christ cometh (ο Χριστος οταν ερχητα). Prolepsis of ο Χριστος and indefinite temporal clause with οταν and the present middle subjunctive ερχητα rather than the more usual second aorist active ελθη as in verse John 7:31, a trifle more picturesque. This is a piece of popular theology. "Three things come wholly unexpected--Messiah, a godsend, and a scorpion" (Sanhedrin 97a). The rulers knew the birthplace to be Bethlehem (John 7:42; Matthew 2:5), but some even expected the Messiah to drop suddenly from the skies as Satan proposed to Jesus to fall down from the pinnacle of the temple. The Jews generally expected a sudden emergence of the Messiah from concealment with an anointing by Elijah (Apoc. of Bar. XXIX. 3; 2Esdr. 7:28; 13:32; Justin Martyr, Tryph. 110).