Yes, engineer candidates should remember core concepts from their degree because IIM Udaipur interviewers often dig into engineering fundamentals to test depth and intellectual rigor. The OP of this thread (ECE engineer from tier 1/1.5 state university) was asked: difference between Fourier Series and Fourier Transform, practical measurement of signal orthogonality, Eigen values, statistics strength.
For chemical: unit operations, process design, reaction engineering. For civil: structural analysis, concrete technology, surveying. For computer science: data structures, algorithms, database systems, operating systems.
Revise 3-4 core subjects in 30-60 minutes each before interview. Practice explaining concepts in layperson terms. Don't get defensive if you don't remember; admit cleanly.
For partial answers (like the OP gave for Eigen values), frame as "Partially, I recall that..." and explain what you remember. Check your eligibility at collvera.