A good way of measuring if your own knowledge, performance and understanding against relevant standards is to request feedback from your line manager. They will be able to give an honest review of your performance and advise you on areas where you may need additional support. This can be done informally or as part of the formal supervision process.
You can also request 360 feedback, which means asking for feedback from everyone that you work with including your clients, their family, co-workers, advocates, other professionals etc.
You will have to learn to be a bit resilient as it can be difficult to hear about where you may be lacking but remember this is for your long-term personal development so it is important to take it on the chin and strive to improve. However, make sure everyone understands that you are asking for constructive feedback and it is not an invitation to have a bitch and a moan and have personal digs at you.
Reflective practice is also a great way to measure your performance.