In plain words
But for those in whom that ignorance concerning the Ātma has been destroyed by jñāna, their jñāna, like the sun, reveals That, the Supreme.
Word for word
But for those in whom that ignorance of the Self has been destroyed by knowledge, for them knowledge, like the sun, reveals That, the Supreme.
The commentators
Bhagavadgītābhāṣyam· bhāṣya
ज्ञानेन तु येन अज्ञानेन आवृताः मुह्यन्ति जन्तवः तत् अज्ञानं येषां जन्तूनां विवेकज्ञानेन आत्मविषयेण नाशितम् आत्मनः भवति, तेषां जन्तूनाम् आदित्यवत् यथा आदित्यः समस्तं रूपजातम् अवभासयति तद्वत् ज्ञानं ज्ञेयं वस्तु सर्वं प्रकाशयति तत् परं परमार्थतत्त्वम् ॥ १६ ॥
In plain words
Ignorance is the blanket thrown over living beings, and under it they lose their way. But for those in whom that ignorance about themselves has been destroyed by viveka — by knowledge that has the Self and nothing else for its object — knowledge works like the sun. As the sun lights up every form there is, so knowledge reveals the whole of what can be known: that supreme, the reality that is the final truth.
Close to the Sanskrit
But by knowledge — that ignorance, covered by which living beings are deluded, that ignorance of one's own self which, in the case of those beings, has been destroyed by discriminative knowledge whose object is the Self — for those beings, like the sun: just as the sun lights up the whole range of forms, in that same way knowledge reveals all the knowable reality, that supreme — the reality that is the highest truth.