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?
Best Answer
No, because it's not part of casting the spell
The trick is in the phrase
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.