Blockers

It's rather a matter of the development team. SM is not their manager. The only thing SM should do is to check is the team aware that they need to talk about blockers and if they don't he/she should coach them

Why does the Scrum Master need to ask anyone - individuals or the team as a whole - about blockers or impediments?

The Daily Scrum is an explicit opportunity for the team to identify impediments that can slow or prevent them from achieving the Sprint Goal. However, the impediment can arise at any point in time. Once the impediment has been identified and raised, whether it's at the Daily Scrum or not, the team should start to resolve it. If they are unsure how to best go about it, the Scrum Master is there to help remove the impediment. This could be in the form of teaching and coaching good practices to resolve it, going off and removing it, or some combination of both.

I think there are some things to keep in mind.

The Scrum Master doesn't need to be at the Daily Scrum. The Scrum Master helps the team understand the intent of the Daily Scrum, makes sure that it happens on a daily basis, and is available to facilitate it upon request. When asked to facilitate, I would expect that the Scrum Master would make sure that the team addresses all of the things that should be addressed, including the identification of impediments.

The Scrum Master is not necessarily responsible for removing all impediments. Although one of the responsibilities of the Scrum Master identified in the Scrum Guide is "removing impediments to the Development Team’s progress", the Scrum Master single-handedly removing the impediments can be a barrier to an empowered, self-organizing team. It's better for the Scrum Master to support the team by coaching the team on ways to identify impediments early and techniques for resolving various types of impediments as they arise.

Should Scrum Master ask development team members individually about blockers they face or ask a general question?

How do you think team self-organization and commitment are best served by the team?

Should Scrum Master ask development team members individually about blockers they face or ask a general question?

If team members knew they were blocked, would they wait to be asked about it at all?

I find it useful to have the team member be specific about their blocker reporting during the daily stand-up for general awareness. Then post-stand-up, the respective team members can tackle the issue.