Even though trade-based evolutions take an exceptionally long time to evolve naturally, they’re still aware of the process. Likewise, they’re often aware of their evolutionary requirements’ relationship to the trading system, especially if you explain, very simply, that they can evolve by trading. (That is to say, they may not know the exact details, but they understand that you’d be telling the truth if you explain that they can evolve through the process.)
With that having been said, they and pokémon with stone-based evolutions have a slight advantage over most other pokémon: they have complete control over when they evolve. As such, they will let you know if they want to evolve through body language. Watch your pokémon for any of the following signs:
- Excitement when you bring up the topic of evolution
- Interest in evolutionary stones (if they evolve by stone) or trading machines or devices (if they evolve by trading)
- Eagerness to train (as to them, training and growing more powerful is still a part of their evolutionary requirements, even if they don’t evolve by battle experience)
If your pokémon shows one or more of these signs, consider sitting down with them and discussing evolution. Then, at your earliest convenience, present them with either your trading device or an evolutionary stone and watch for their reaction. If they seem excited and ready, then it’s time to help them evolve. If not, leave them alone and consider discussing evolution with them at a later time.
In other words, you’ll be able to tell whether or not your pokémon is ready to evolve simply because they’ll tell you so; it will just be a nonverbal confirmation.
The Pokédex According to Bill 