Navigation Componentの依存関係

app-build.gradle

...
// add plugin if you use safe args.
apply plugin: "androidx.navigation.safeargs.kotlin"
...

android {
  ...
  // Enable Java8 if you use safe args
  compileOptions {
        sourceCompatibility JavaVersion.VERSION_1_8
        targetCompatibility JavaVersion.VERSION_1_8
  }
  kotlinOptions {
    jvmTarget = JavaVersion.VERSION_1_8.toString()
  }
  ...
  dependencies {
      // add dependencies for navigation component (nav_version is defined in 'build.gradle' of project root)
      implementation "androidx.navigation:navigation-fragment-ktx:$nav_version"
      implementation "androidx.navigation:navigation-ui-ktx:$nav_version"
  }
  ...
}

build.gradle

buildscript {
    ...
    // set latest version
    ext.nav_version='2.1.0'
    ...
    dependencies {
        ...
        // add plugin dependency if you use safe args
        classpath "androidx.navigation:navigation-safe-args-gradle-plugin:$nav_version"
    }
}

See document for more detail.