Prior to doing the actual on-the-water assessment for the SLC and SLC-p with a NauticEd assessor, you are well advised to go through the self-assessment to determine any weaknesses. You then enter the email address of your instructor into the document, which will be sent to your assessor. This helps the assessor to determine how long the assessment will take on the water.
It is in your interest to be honest - the assessor's job is to find weaknesses (if any) to help you and the assessor determine your true competence. Given enough time, the assessor could train on those weaknesses. However, if not enough time is allotted, you could leave the assessment having not yet passed.
For example, if you are not fully competent on say Mediterranean Mooring, training would last probably an extra 3 hours on top of the pure assessment time. This lends to another day.
Keep in mind that you want the assessor to find weaknesses. The last thing you want is to get away with something just so that you could pass and then have the issue show up when you are in command and not be able to handle it, causing damage to the boat, injury, or at the very least embarrassment.
The self-assessment documents for students are in your curriculum when you sign in as a student.
For schools and instructors, the self-assessments are on the pro-site under Resources and Libraries > School & Instructor Set-up, Assessment, and Training Documents > Practical Training and Assessment