、「」。
Frankly speaking, I think this 'conspiracy theory' is nonsense.
Literal
Clearly say, this 'conspiracy-theory' [topic-は] nonsense [copula-だ][quotative-と] think.
ハッキリ言って is a discourse-prefacing set phrase: 'frankly / to put it plainly / not to mince words.' The te-form of 言う functions as a fixed adverbial framing the whole sentence, not as a connected action. ナンセンス is a katakana loanword used more lightly than in English — closer to 'ridiculous / absurd' than a technical logical-nonsense claim. The single brackets 「」 around 陰謀説 signal distanced, ironic quotation — the speaker is refusing to fully endorse the label.