No, I think you could just say; 'Greet your father properly as you've been taught.'

No, it is not necessary to use "so" at the end of the sentence. Adding the word "so" to the end of the sentence changes the grammar of the sentence and requires using a comma to divide the sentence into two clauses. The choices are: 1. "Greet your father properly as you've (you have) been taught do do" 2. "Greet your father properly, as you've (you have) been taught to do so". In the second sentence, the word "so" functions as a pronoun that refers to "greet your father properly". Both sentences are equally good.

Bill's answers that I have seen are good. Yet on this I came to a different conclusion. IN the first, and Charlie's I assume the "so" can be either refering to "properly", that is "hjow to greet" or to "you have been taught", that is do it, rather than how. . In the second, I read it as only possibly refering to "because you have been taught". In the end the difference is inconsequential. . If we remove the "properly" it gets more different for me, highlighting the diference. 'Greet your father as you've been taught to do.' - could be "greet him", or "greet him the same way as taught" 'Greet your father as you've been taught to do so.' - only means beacuse you have been taught. No sense of "how". I may be wrong.