Here is my recommendation for when you're asked to do a particular procedure of which you are not familiar.
Step 1: Check your facilities Policy & Procedure Book
. If the agency that you work for says that you can't do it, well then don't do it. Easy as that...
Step 2: Check your state's Nurse Practice Act.
Make sure that what you are asked to do is within your scope of practice. Use common sense with this one, if your asked as a CNA to take a patient's apical pulse then obviously this is within your scope of practice (even if you personally haven't done it before) but doing a sterile procedure like a dressing change or inserting an catheter is something that you need to check on before you try it.
Step 3: If the task/procedure is within your scope of practice, you must then ask yourself: Have you ever seen this done before? Do you know the proper steps to performing the task?
If you do not know the steps or are not comfortable doing the procedure by yourself then seek out the appropriate resource to assist you with the task until you feel that you are competent and comfortable doing said task alone.
I am not familar with your state's Nurse Practice Act but I would be very wary as a CNA doing a sterile procedure like inserting a cath. or giving any sort of medication unless I was absolutely sure that doing so was not illegal and that I am fully aware of how to do the procedure properly and the risks involved. It's better to be safe than sorry, CYA as they say.