regex to match question sentences in long text

In your example you use [a-zA-Z]+, but you might extend that to matching 1 or more word characters using w+

This part at the end of the pattern s\? matches an expected whitespace char followed by an optional backslash.

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To match multiple words, you can optionally repeat the pattern to match a word preceded by 1 or more whitespace characters.

You one option is to use

d.s+w+(?:s+w+)*s*?

Explanation

• d. Match a single digit (for 1 or digits use d+)
• s+w+ Match a . and 1+ whitspace chars and 1+ word chars
• (?:s+w+)* Optionally repeat 1+ whitspace chars and 1+ word chars
• s*? Match 0+ whitespace chars and a question mark.

Regex demo

A broader match might be matching at least a single time any char except a question mark or whitespace char after the digit, dot and whitespace:

d.s+[^s?]+(?:s+[^s?]+)*?

Regex demo