Your Jekyll site is static, so calculating what post is popular using visitor data will probably be more trouble than it is worth. I am sure there are articles on how to do that, but I doubt it is easy
Here are some options you can try out, including some videos I created on the topic:
Option #1: Display the latest post
{%- for post in site.posts limit: 1 -%}
{{- post.title -}}
{%- endfor -%}
Option #2: Display what you have decided is a featured or popular post
In the front matter of the post, create a custom variable called featuredPost
(you decide on the name) and then write code that looks like this:
---
layout: post
date: 2020-08-10 12:30:00 -0700
title: This is a great featured post
featuredPost: true
---
Welcome to this great post!
In the page that displays the post(s), use the custom variable:
{%- assign fp = site.posts | where: 'featuredPost', true -%}
{%- for fp in site.posts -%}
{{- post.title -}}
{%- endfor -%}
I created a 2-part video series on how to add a featured image to your site. There is also a 3-part series on creating reusable code to display a unique featured post, which is what you are after.
Start with this video and then keep going through the playlist:
Or, reference my two posts with included video links here on Jekyll Talk:
Here’s the GitHub repo:
And here is an example of what the code looks like: