Generally speaking, it is difficult to get job seekers to pay for anything. But if the product offers value, you can sell to them. Two of the more viable viable products I can think of are ebooks and courses.
When I ran AllCountyJobs, I wrote ebooks for each of the county based sites I operated. Each doc listed the area’s top employers, career advice, local job resources and more. I sold 5-10 of these per month for ten bucks each. Not a lot of money, but it helped make my sites more profitable each month.
But even if you run a national niche site you can do the same thing. Create a pdf guide for “working in (your) industry” and sell it for $10 bucks. People will buy it as long as the content is of value. You can even use a site like Gumroad.com to sell your ebooks under a subdomain. Gumroad is free, but costs just $10 a month if you want extra features including a custom domain.
An online course that targets your niche is also a great idea. You can use services like Teachable.com to create one and charge money for it. The good thing with courses is you can charge much more than ebooks. If you created a course for something like “How to Get a Job in (insert) Industry” you could easily charge $99-$299 depending on the popularity of your niche.
For example, a course like how to get a job in major league baseball is sure to be a hit. Or perhaps even an industry like Cannabis or casinos.
I like to see job boards have multiple revenue streams beyond just job postings. Sites like JoeProduce.com are a good example of that through its resume service that is a significant portion of its income.