Some spells and abilities that investigate may require targets. If each target chosen is an illegal target as that spell or ability tries to resolve, it won’t resolve. You won’t create any Clue tokens.

Clue is an artifact type. Even though it appears on some cards with other permanent types, it’s never a creature type, a land type, or anything but an artifact type.

If an effect refers to a Clue, it means any Clue artifact, not just a Clue artifact token. For example, you can sacrifice Wrench to pay for Alquist Proft, Master Sleuth’s activated ability.

You can’t sacrifice a Clue to pay multiple costs. For example, you can’t sacrifice a Clue token to activate its own ability and also to activate Alquist Proft, Master Sleuth’s ability.

Except in some very unusual cases, the card each player reveals is the one they’ll draw.

There’s no window for you to cast spells after untapping all lands you control but before the “you can’t cast spells” portion of Innocuous Researcher’s last ability takes effect. Once that ability resolves, it doesn’t matter whether Innocuous Researcher stays on the battlefield; you’ll still be unable to cast spells until your next turn begins.

Some abilities trigger “whenever you sacrifice a Clue”. Those abilities trigger whenever you sacrifice a Clue for any reason, not just to activate a Clue’s activated ability.