Example

gistfile1.txt

// Declarative Pipeline
pipeline {
    agent { label "builder" }
    options {
        timestamps()
        skipDefaultCheckout()
        ansiColor colorMapName: 'XTerm'
        buildDiscarder(logRotator(numToKeepStr: '10'))
    }
    stages {
        stage ('Stage 1') {
            steps {
            echo "${ghprbActualCommitAuthorEmail}"
            }
        }
    }
}

Try echo "${env.ghprbActualCommitAuthorEmail}"