他/她是某大学的著名教授，享有很高的学术造诣 He/she is a well-kown professor of a university who enjoys a high level of academic attainments.

是某大学著名的老教授，学术上有很高的水平。means"he or she is a well-known experienced professor in the college and is a leading researcher in his or her field of study.

某大学 a certain university

1.某人＝someone “某大学” means 'an university', not 'the university'. 学术上＝academically 2.This sentence is lack of a subject. I assume the subject is '他'. This sentence translate to English is "He is a famous professor of an university, and he has a high academic attainments.

某 means some/in a university; 学术上 means academically 是某大学著名的老教授，学术上有很高的水平 so this sentence means: he is an old professor in a university (we do not know which university he is in), who has high academic levels/knowledge