Should I give an assessment to DevOps Candidate
Yes, there absolutely should be an assessment, however it would be a good idea to agree upfront with one of the few DevOps people you know to validate the content and results.

Regarding the contents of the assessment, there are some questions still remaining after your edits. Key one is how your operations are done. Possible options are: you already have someone doing your server infrastructure and operations and looking for a purely CI/CD person, or you do not have good operations support (i.e. developers doing that and you're unhappy) and you need DevOps person to do server management too. Note, that if it's the later case, you'd probably need more than person over time but you need somebody senior to start with.

Note, that for larger organizations you'd find more specialization within DevOps (i.e. things like Release Management, DevSecOps and others), but for smaller companies those two - CI/CD vs Infra Operations are two main ones in my experience. You still need to keep those differences in mind if you're considering taking someone from a larger company.

Now, after answering those questions, you need to first establish the seniority level of a person you're looking to hire. If it's your first DevOps person - you would probably want somebody more senior, but it depends on other people in your existing team. Next you scope your assessment to the on-job tasks. My take - always give take-at-home assignments, I usually give it to candidates over weekend and I make sure they take no more than 3-4 hours.

For CI/CD case you may ask them for a simple CI pipeline in their tool of choice, built from scratch over some sample project. You should add extra questions about failure handling, parallelizing, caching, handling of automation tests.

For CI/CD + operations case you should add tasks about shell scripting, cloud security, terraform.

Also for the first DevOps / senior person it's always a good idea to add some questions about interacting with other teams. I.e. what developers would need to do and how the interaction process with them should be built.

Again, start with one of the few DevOps people you know and get them onboard as a consultant to assess and hire that first person, otherwise you're taking a lot of chances there - and DevOps is a pretty sensitive part of your business.