In plain words
But that jñāna which sees in all beings, as separate, many different selves of different kinds, know that to be rājasa.
Word for word
But that knowledge which knows, as separate, in all beings, many different selves of separate kinds, know that knowledge to be rājasa.
पृथक्त्वेन तु यज्ज्ञानं नानाभावान् पृथग्विधान्वेत्ति सर्वेषु भूतेषु तज्ज्ञानं विद्धि राजसम्
Other commentaries
The commentators
▸Bhagavadgītābhāṣyam
यानि द्वैतदर्शनानि तानि असम्यग्भूतानि राजसानि तामसानि च इति न साक्षात् संसारोच्छित्तये भवन्ति —
पृथक्त्वेन तु भेदेन प्रतिशरीरम् अन्यत्वेन यत् ज्ञानं नानाभावान् भिन्नान् आत्मनः पृथग्विधान् पृथक्प्रकारान् भिन्नलक्षणान् इत्यर्थः, वेत्ति विजानाति यत् ज्ञानं सर्वेषु भूतेषु, ज्ञानस्य कर्तृत्वासम्भवात् येन ज्ञानेन वेत्ति इत्यर्थः, तत् ज्ञानं विद्धि राजसं रजोगुणनिर्वृत्तम् ॥ २१ ॥
In plain words
Whatever views see duality, those views have not arrived at the truth: they belong to rajas and to tamas. So they do not, of themselves, cut saṃsāra out at the root —
'Separately' means: by difference, body by body, as one other thing after another. The knowledge that looks across all beings and knows them like that — manifold entities, selves cut apart from each other, each of its own kind, its own sort, its own set of marks — that is what the word carries. And since knowledge is never the doer, 'knows' has to mean 'one knows by means of that knowledge'. Know that knowledge as rājasa: nothing but rajas, working itself out.
Close to the Sanskrit
Those visions of duality which there are — those, having become incorrect, being rājasic and tāmasic — thus they do not directly serve for the uprooting of saṃsāra —
'Separately' — that is, by difference, body by body, by otherness: that knowledge which knows, that is, fully cognizes, the manifold entities — the divided selves, of separate kinds, of separate sorts, of differing marks; such is the sense — in all beings; and since knowledge cannot be an agent, the meaning is 'by which knowledge one knows'; know that knowledge to be rājasa, produced out of the guṇa of rajas.