I am on day 21 of my cycle and my endometrial thickness is 9.4mm. What is the implication of this as regards ovulation?

Unclear. For a women with regular menstrual cycles ovulation would normally occur around day 14. An endometrial thickness of 9.4mm after ovulation would be normal, and encouraging. A better idea about ovulation can be obtained from looking at the ovaries near the time ovulation is happening.
Very little. The endometrial thickness does not depend on ovulation to progress. It only requires estrogen.