I'll probably have finished reading that novel by next Sunday.
Literal
Next-week [possessive-の] Sunday [by-までには] that novel [object-を] read-[completion-てしまっている] [probably-だろう].
A compact past-perfect construction in Japanese: 読んでしまっている = 読む ('read') + ~てしまう ('complete') + ~ている (state) = 'be in the state of having finished reading.' Paired with だろう for future probability. Japanese constructs the English perfect tense this way — via auxiliary stacking.