_{Inspired by this question on how to improve the chances of casting spells from scrolls.}

Improved Abjuration, the School of Abjuration wizard's 10th-level feature, states (PHB, 115):

Beginning at 10th level, when you cast an abjuration spell that requires you to make an ability check as a part of casting that spell (as in counterspell and dispel magic), you add your proficiency bonus to that ability check.

The description for the spell scroll magic item states:

If the spell is on your class’s spell list but of a higher level than you can normally cast, you must make an ability check using your spellcasting ability to determine whether you cast it successfully.

If a 10th-level Wizard (who can cast up to 5th-level spells) finds a spell scroll for an abjuration spell of 6th level or higher (such as globe of invulnerability) and attempts to cast it, they will need to make an ability check.

Does the wizard get to apply their proficiency bonus to that check thanks to the Improved Abjuration feature?

No, because it's not part of casting the spell

The trick is in the phrase

part of casting that spell

Because you need to roll a check to see if you can even cast it at all (determine whether you cast it successfully), the check is not part of the actual casting of the spell (i.e. the spell says make an ability check somewhere in its description), and, RAW, therefore will not get a bonus from Improved abjuration.

Yes, 5e reads as plain English

There is no reasonable English language reading that a check "to determine if you cast [the spell] successfully" is not a "[...] check as part of casting the spell".

Barring rules stating otherwise, 5e reads as plain English.

Balance wise, this is not going to be hugely significant; it will at most double the utility of "too high" level scrolls, and scrolls are either pure GP or handed out by DM fiat.

Sense wise, you are a master Abjurer, being able to cast Abjuration spells from spell scrolls more reliably is reasonable.

Rule of Cool wise, if a player character has an ability, you should default to interpreting it generously unless there is a reason not to.

A DM could rule otherwise. For example, they could claim that the spell isn't requiring the ability check, but the spell scroll is. That kind of hair-splitting is a reasonable justification when there is any of Sense, Balance or even Rule of Cool reasons to say no.