Squire's Devotion — ruling 1

You need a creature for Squire's Devotion to target as you cast it. There's no way to have it enter the battlefield attached to the Vampire token it'll create.

Squire's Devotion — ruling 2

If the creature this Aura would enchant is an illegal target by the time Squire's Devotion tries to resolve, the Aura spell doesn't resolve. It won't enter the battlefield, so its ability won't trigger.

Squire's Devotion : règles, fonctionnement et interactions (MTG)

Squire's Devotion is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

Enchant creature Enchanted creature gets +1/+1 and has lifelink. When this Aura enters, create a 1/1 white Vampire creature token with lifelink.

How it works : Squire's Devotion

Original English text — Wizards of the Coast / Scryfall

#1January 19, 2018· Wizards of the Coast
You need a creature for Squire's Devotion to target as you cast it. There's no way to have it enter the battlefield attached to the Vampire token it'll create.
Card named in this ruling
Vampire
#2January 19, 2018· Wizards of the Coast
If the creature this Aura would enchant is an illegal target by the time Squire's Devotion tries to resolve, the Aura spell doesn't resolve. It won't enter the battlefield, so its ability won't trigger.
No other card is named in this ruling.