How can I calculate my student son's net income and the amount of non-refundable tax credits with only his T4 and T2202A, and no info from previous returns?

The easiest way would be to do his tax return first, and then you’ll have the correct information available to put into your tax return. If you want to transfer tuition from him, you will need additional information from his return, too.

Here is how to enter dependants in TurboTax Online: https://turbotax.community.intuit.ca/replies/2928190

Here is a FAQ listing what tuition, education, and other expenses can a student claim, as well information about tuition transfer: https://turbotax.community.intuit.ca/replies/2648040