What then if ye should behold (ean oun theōrēte). No “what” in the Greek. Condition of third class with ean and present active subjunctive, “if ye then behold.”
Ascending (anabainonta). Present active participle picturing the process.
Where he was before (hopou ēn to proteron). Neuter articular adjective as adverb (accusative of general reference, at the former time as in Joh 9:8; Gal 3:13). Clear statement of Christ’s pre-existence in his own words as in Joh 3:13; Joh 17:5 (cf. 1:1-18).