Sorcerous Spyglass
Artifact
As Sorcerous Spyglass enters the battlefield, look at an opponent's hand, then choose any card name.
Activated abilities of sources with the chosen name can't be activated unless they're mana abilities.
Illustrated by
Throne of Eldraine Promos#233pRareEnglishLegality
Rulings
You can choose any card name, even if that card doesn't normally have an activated ability. You're not limited to the names of cards you saw in the opponent's hand.
You can't choose the name of a token unless that token has the same name as a card.
Activated abilities contain a colon. They're generally written "[Cost]: [Effect]." Some keyword abilities (such as equip) are activated abilities and will have colons in their reminder text. Triggered abilities (starting with "when," "whenever," or "at") are unaffected by the last ability of Sorcerous Spyglass.
An activated mana ability is one that produces mana as it resolves, not one that costs mana to activate.
Sorcerous Spyglass affects cards regardless of what zone they're in. This includes cards in hand, cards in the graveyard, and exiled cards.