I am a PH'D student in Finance at Syracuse University. I have been a TA for six years. I work twenty hours per week. Can that experience be counted as my work experience? How many years should I count? Which occupation and ETF should I choose?

Yes, your part-time work experience as a TA can be counted. You need to have 4 year full-time work experience (over 35 hours/per week). Occpation is Post-secondary Teaching and Research Assistant. NOC code is not necessary.