«الَّذِينَ يَعْلَمُونَ»
Those who have knowledge.
«أَنْ يَرَى مُبْصِرٌ وَيَسْمَعَ وَاعٍ»
That one who sees should see, and one who hears should hear.
The first expression characterizes persons by knowledge; the second evokes acts of perception and, in its context, indirectly praises someone's wide reputation. Their shared feature is that an unspoken object should not automatically be treated as one particular ellipsis.
Their difference is the rhetorical aim: contrastive classification in the Qur'anic expression versus indirect praise in the poetic passage.