Yes, but the effect specifically says that only the attack Jump About is boosted. So, if you switch for another Mankey is ok, but not for other Pokémon cards. The effect boosts only Jump About attack, not every attack. It does not say " the next turn every attack from this Pokémon do 50 more damage", so Ninja Boy will not pass the boost for other attacks.Actually, I believe it does. There was a rule a few years ago explaining this type of situation. Cards used to say the pokémon's name instead of "this pokémon". They started using the term "this pokémon" because these type of effects do pass to the new pokémon. The attack refers to the pokémon on which the effect is active and ninja boy passes effects, therefore, "this pokémon" will be the new pokémon you switched Mankey for.
EDIT: the text says that, next turn, Jump About does 50 damage, not +50 damage. It's 50 instead of 10, so it's not even a real boost. If you use Ninja Boy to another Pokémon who's not Mankey, which attack inflicts 50 instead of its original damage? No, guys, really... Ninja Boy won't work unless you don't switch between Mankeys, and I don't know why one would switch between them, lol.
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