What ... whom - The prophet accosts Shebna at the very place where he was building a grand sepulcher for himself and his family (compare Isa 14:18; Gen 23:1-20; Gen 49:29; Gen 50:13). “What (business) hast thou here, and whom hast thou (of thy family, who is likely to be buried) here, that thou buildest,” etc., seeing that thou art soon to be deposed from office and carried into captivity? [Maurer].
on high - Sepulchres were made in the highest rocks (2Ch 32:33, Margin).
habitation for himself - compare “his own house” (Isa 14:18).