たしかに/なるほど~かもしれない => might; perhaps N3
Speculation
かどうか => whether or not ~ N4
たらどうですか => why don't you; how about ~ N4
Invite and advise
どうして => why; for what reason; how N5
どうも ... そうだ/ ようだ/ らしい => It seems, probably N3
Speculation
...どおし => Throughout N3
Continuous
もしかしたら…か => perhaps; maybe; perchance; by any chance ~ N4
Speculation
どんなに…だろう(か) => how…!; what…! N3
Emphasis on degree
はどうですか => how about; how is N5
どうにかする => find a way to N2
Conditions (sufficient conditions)
はどうですか => how about; how is N5
Doubt
どうしても => no matter what; at any cost; after all ~ N3