Navisworks alone provides you with limited sorting options. If you want to sort by a field (in your case - Level), then you would have to export the clash report as an .XML file. Then you can open that in Excel and sort.
If you want better control over your reports, you need to look at a third-party tool like iConstruct. It has additional features. Reach out to Rob at iConstruct Rob.Gadbaw@iconstruct.com and ask him to show you his reporting tools. I would also suggest you ask him to show you their clash grouping tools. It will make your life easier.
There are some other tools like Revizto and BIMTrak that can also help you manage your issues.
Please mark this response as "Accept as Solution" if it answers your question.
Patrick Davis
TwitterLinkedInBlog
