For Skill Worker applicant, all their higher education have to be assessed, or only the highest one? e.g., one could have Bachelor, Master and PH.D degrees obtained outside of Canada. the Bachelor and Master have been obtained more than 10 years ago. In this case, do all degrees need to get ECA or only the PH.D assessment is required?
You have to have at least ONE "completed" Canadian equivalent qualification at a post-secondary level. In this case, if you believe your Phd will be comparable to a completed Canadian doctorate degree you may submit it for equivalence and be done with. If, for example, the ECA finds that your doctorate is only equivalent to, let's say, 3 years of study towards a Canadian doctorate, then this is a "NOT COMPLETED" study.
There is no requirement that you submit for equivalence all the degrees you have had as long as you fulfill #1 above.
Remember, you will only receive points for the completed post secondary Canadian equivalent education that has the ECA attached alongwith the copy of the degree and transcripts. This means that if you have a Bachelor's and a Masters and you submit the Bachelors (which has been found to be equivalent to a completed Canadian Bachelor's) you will only get points for the Bachelor's (and not the Masters). If you want higher points, get your Master's assessed for ECA.