@alexamae Hi! I will try to answer your questions based on our understanding of the TRA guidelines, before we worked on the TRA documents as well as its requirements because initially we planned to apply for assessment as ICT Customer Support Officer.
On your first question, it means you will list down your job duties based on you own words which is the same when you are preparing your resume.
On evidence of employment of the person signing the Employment Statement, I have asked that same question here before and @razlem712 said he provided calling card and company ID of the person who signed his Employment Statement. Maybe if you have a letter from your supervisor confirming your permanent employee status after probationary period will help, in case you have one.
Not really sure with your third question, in our case, the person who signed was his supervisor during his entire stay with the company. If I were you, to be sure, I will request two separate Employment Statement.
Regarding payslips, we would have provided ITR and those periods without ITR yet we would have submitted payslips, e.g. Employment period is Jan 2009 to July 2012, For 2009,2010 and 2011 we have ITR and Jan to Jul 2012 we have payslips.
Hope somehow these will help you.