In plain words
The wise see with equal vision a learned and humble brahmin, a cow, an elephant, a dog, and an outcaste who cooks dogs.
Word for word
In a brahmin endowed with learning and humility, in a cow, in an elephant, and even in a dog and in a dog-cooker, the wise [are] seers of the same.
The commentators
Bhagavadgītābhāṣyam
येषां ज्ञानेन नाशितम् आत्मनः अज्ञानं ते पण्डिताः कथं तत्त्वं पश्यन्ति इत्युच्यते —
विद्याविनयसम्पन्ने विद्या च विनयश्च विद्याविनयौ, विनयः उपशमः, ताभ्यां विद्याविनयाभ्यां सम्पन्नः विद्याविनयसम्पन्नः विद्वान् विनीतश्च यो ब्राह्मणः तस्मिन् ब्राह्मणे गवि हस्तिनि शुनि चैव श्वपाके च पण्डिताः समदर्शिनः । विद्याविनयसम्पन्ने उत्तमसंस्कारवति ब्राह्मणे सात्त्विके, मध्यमायां च राजस्यां गवि, संस्कारहीनायां अत्यन्तमेव केवलतामसे हस्त्यादौ च, सत्त्वादिगुणैः तज्जैश्च संस्कारैः तथा राजसैः तथा तामसैश्च संस्कारैः अत्यन्तमेव अस्पृष्टं समम् एकम् अविक्रियं तत् ब्रह्म द्रष्टुं शीलं येषां ते पण्डिताः समदर्शिनः ॥ १८ ॥
In plain words
Those whose ignorance about the Self has been burned away by knowledge — the wise — how exactly do they see what is real? That is what is said next —
'Endowed with learning and discipline' means having both learning and discipline together — discipline meaning self-restraint. A brahmin who has both — learned and disciplined at once — such a brahmin, and a cow, and an elephant, and a dog, and even an outcaste — the wise see all of them equally. In the highly refined, sāttvic brahmin; in the middling, rājasic cow; and in the crude, purely tāmasic elephant and the like — despite all the impressions left by sattva, rajas, and tamas — they see one thing, utterly untouched by any of it: the same changeless Brahman, one and undivided. Seeing that everywhere is simply what these wise people do. That is what it means to 'see equally.'
Close to the Sanskrit
Those in whom the ignorance regarding the Self has been destroyed by knowledge — those wise ones, how do they see the truth? Thus it is said —
'Endowed with learning and discipline': learning and discipline [together] are 'learning-and-discipline'; 'discipline' means restraint; a brahmin who is endowed by those two, learning and discipline, [i.e.] 'endowed-with-learning-and-discipline,' [meaning] learned and disciplined — 'in that brahmin, in the cow, in the elephant, in the dog, and indeed in the outcaste, the wise see equally.' In the brahmin endowed with learning and discipline, possessed of the highest refinement, who is sāttvic; in the middling, rājasic cow; and in the elephant and the like, devoid of refinement, utterly and purely tāmasic — by the qualities beginning with sattva, and the resulting impressions born from them, likewise the rājasic, and likewise the tāmasic impressions, utterly untouched, the same, one, changeless — that Brahman is the habit of whom to see; they are 'the wise who see equally.'