Check the "Show question numbers" option present under survey option.

It's under the "Survey Options" tab:

Cool, thank you both. But one follow-up question:
Some questions are not questions, so they don't have question numbers. For example, in my survey, there is a text description question.

In preview, it shows up as:
Looks weird and ugly. How to fix this?

Check this

where should I paste it to? I can't find "Paste the below code in the Header(edit) -> "<>" source view"

https://www.qualtrics.com/community/discussion/comment/29113#Comment_29113Go to look and feel tab -> General -> Header(edit) -> "<>" source view"

This setting only works for my 1st block. My 2nd, 3rd block still have the dots. How to fix it? I can fix it by just move all 2nd & 3rd block questions to 1st block, i.e., disabling 2nd and 3rd blocks. I don't know when I should use blocks. My original idea is that some questions like collecting demographic information are distinct from the survey questions. So I used block. But I found using page break can also make it. What do you think?

https://www.qualtrics.com/community/discussion/comment/29120#Comment_29120Ideally this should not happen, try this solution.