Because (dioti). Gives the reason (dia, hoti like our “for that”) for the revelation of God’s wrath.
That which may be known of God (to gnōston tou theou). Verbal adjective from ginōskō, either “the known” as elsewhere in N.T. (Act 1:19; Act 15:18, etc.) or “the knowable” as usual in ancient Greek, that is “the knowledge” (hē gnōsis) of God. See Phi 3:8. Cf. same use of the verbal chrēston in Rom 2:4, ametatheton in Heb 6:17.
Manifest in them (phaneron en autois). In their hearts and consciences.
God manifested (ho theos ephanerōsen). First aorist active indicative of phaneroō. Not mere tautology. See Rom 2:14-16.