Yahoo資訊看到Mary took my last piece of candy.👉 Mary 為主詞，took 為動詞，last piece of candy 為補語。last piece of candy 是受詞吧？

This pattern from "Yahoo" is for the verb "took".The subject complement may be a noun, an adverbial adjunct.
Mary took---------Subject+BE(took)
last piece of candy-----subject complement/adjunct,(adjunct is possible)(subject complement is possible)