If ye know (ean eidēte). Third-class condition again with ean and second perfect active subjunctive of oida. If ye know by intuitive or absolute knowledge that Christ (because of 1Jo 2:28) is righteous, then “ye know” or “know ye” (ginōskete either indicative or imperative) by experimental knowledge (so ginōskō means in contrast with oida).
Is begotten (gegennētai). Perfect passive indicative of gennaō, stands begotten, the second birth (regeneration) of Joh 3:3-8.
Of him (ex autou). Plainly “of God” in 1Jo 2:9 and so apparently here in spite of dikaios referring to Christ. Doing righteousness is proof of the new birth.