What is the expiation for not fulfilling a covenant made with Allah to study daily?

A covenant on something that is not an act of worship, such as daily study, falls under the ruling of an oath. Therefore, it is not obligatory to fulfill it. Rather, the one who made the covenant has the choice between performing it or offering expiation for an oath. This covenant is dissolved by breaking it the first time, and the expiation is not repeated unless a phrase indicating repetition is uttered (such as "every time") or repetition is intended.