Does Saba Publisher Online support book marking?

If you are publishing to AICC/SCORM then it should be automatic through your LMS.

If you are publishing to HTML, you can enable the Variable Manager's option Retain test answers between sessions and also keep track of users taking your course by using variables. Keep in mind that Saba Publisher Online is using cookies to keep this information and will only be stored if they come back to the test from the same machine.