In plain words
Calmness, control of the outer senses, Tapas, purity, patience, straightforwardness, Jñāna, Vijñāna, and faith in sacred truth are brāhmaṇa-Karma born of Svabhāva.
Word for word
Calm of mind, restraint of the senses, tapas, purity, forbearance and straightness also, knowledge, realisation, faith: the duty of the brāhmaṇa, born of svabhāva.
The commentators
Bhagavadgītābhāṣyam
कानि पुनः तानि कर्माणि इति, उच्यते —
शमः दमश्च यथाव्याख्यातार्थौ, तपः यथोक्तं शारीरादि, शौचं व्याख्यातम् , क्षान्तिः क्षमा, आर्जवम् ऋजुता एव च ज्ञानं विज्ञानम् , आस्तिक्यम् आस्तिकभावः श्रद्दधानता आगमार्थेषु, ब्रह्मकर्म ब्राह्मणजातेः कर्म स्वभावजम् — यत् उक्तं स्वभावप्रभवैर्गुणैः प्रविभक्तानि इति तदेवोक्तं स्वभावजम् इति ॥ ४२ ॥
In plain words
But which actions are these? Here is the answer —
Śama and dama mean just what they meant before; tapas is as already explained — bodily austerity and the rest; śauca, too, has already been explained. Kṣānti simply means forbearance; ārjava simply means straightforwardness. Jñāna and vijñāna need no further gloss. Āstikya means holding scripture as true — real, living faith in what scripture teaches. And 'brahma-karma' is simply the brahmin's own duty, born of his own nature — the very same thing already meant, earlier, by 'distributed by the guṇas born of one's own nature'; here it is just called 'svabhāvaja', born of nature.
Close to the Sanskrit
'But which are those actions?' — thus; it is said —
Śama and dama have the meaning already explained; tapas is as already stated — bodily and so forth; śauca has been explained. Kṣānti means forbearance; ārjava means indeed straightforwardness; jñāna and vijñāna; āstikya means the state of being a believer, the state of having faith, in the meanings of scripture; 'brahma-karma' means the duty of the brahmin class, born of its own nature — that which was said, 'distributed by the guṇas born of one's own nature', that very thing is here said as 'svabhāvajam'.