Final answer:
The sentence 'Joshua's gift is a toy train' has a predicate noun, which is 'a toy train' as it identifies the subject of the sentence.
Eplanation:
The sentence 'Joshua's gift is a toy train' contains a predicate noun. In the sentence, 'Joshua's gift' is the subject, and 'is' is the linking verb that connects the subject with the subject complement. The phrase 'a toy train' acts as the subject complement, more specifically a predicate noun, because it is a noun that identifies the subject of the sentence.
A predicate adjective would instead describe a characteristic or attribute of the subject (e.g., 'The train is red.').