مَا طَالِبٌ غَائِبٌ — No student is absent (with the intended general negation).
مَا: non-governing negative particle in this reading.
طَالِبٌ: nominative indefinite mubtadaʾ.
غَائِبٌ: nominative khabar.
Do not merge this analysis with «لَيْسَ طَالِبٌ غَائِبًا»: laysa is a defective verb that makes its predicate accusative.