إِنَّ الطَّالِبَ مُجْتَهِدٌ
Translation: Indeed, the student is diligent.
إِنَّ: emphatic and accusative-governing particle.
الطَّالِبَ: accusative ism inna, with fatḥa.
مُجْتَهِدٌ: nominative khabar inna, a single-word predicate.
“Mufrad khabar” means “not itself a clause or quasi-clause,” not necessarily singular in number.