Want to live like the rich and famous? Petronius satirises the high life in opulent Rome

Hic nescio quid boni debet esse.

This must be something good, I don’t know what.

Hic (this) is a demonstrative pronoun.

Debet (must be or ought to be) is the third person singular present indicative form of "debere."

Nescio quid (something) from "nescio" (I do not know), and "quid" (what).

Boni (good) is the genitive singular form of "bonus," used to describe the quality of "quid".

Esse (to be) used with "debet" to complete the expression "must be."