Explanation:
The question is about Sam Watson, a character from the novel "Their Eyes Were Watching God" by Zora Neale Hurston.
This novel is filled with vernacular language, as a part of the setting of the story.
Questioning means doubting a validity of something, demanding a proof, querying.
Sam Watson, in this particular situation, used the term "questionizin" as a synonim for "asking" ("Ah'm questionizin' you!")
Although both words have the same root (question) their meanings slightly differ, as shown, but in spite of that difference, Sam's sentence can be understood in a proper context.