What type of diagramming line goes before a predicate nominative?

The type of diagramming line that goes before a predicate nominative is a horizontal line. This line connects the predicate nominative to the verb, indicating that the predicate nominative renames or identifies the subject.

Here's a simple example:

Sentence: The cat is a pet.

Diagram:

```

________________________

| |

| The cat is a pet |

|________| |___________|

```

In this diagram, the horizontal line connects the predicate nominative "pet" to the verb "is".

Remember: A predicate nominative is a noun or pronoun that follows a linking verb and renames or identifies the subject. It's important to distinguish a predicate nominative from a direct object, which receives the action of a verb.