List all enqueued scripts and styles on the current page. This won't work as an REST API endpoint, unfortunately. If that's your goal, use Frontity's head tags plugin and disable filtering of scripts and styles.

wp-list-enqueued-scripts-styles.php

global $enqueued_scripts;
global $enqueued_styles;

function sg_format_asset_url( $src, $ver ) {
	// Fallback to WP version, if not set
	$ver = $ver ? $ver : get_bloginfo( 'version', 'display' );

	// Append site root URL, if missing
	$url = strpos( $src, get_home_url() ) !== false ? $src : get_home_url() . $src;

	// Cache busting
	$url .= '?ver=' . $ver;

	return $url;
}

function sg_walk_dependencies( $asset, $is_script ) {
	global $wp_scripts;
	global $wp_styles;

	$urls = array();
	if( $asset->deps ) {
		foreach( $asset->deps as $handle ) {
			// Get object for this dependency
			$dep = $is_script ? $wp_scripts->registered[$handle] : $wp_styles->registered[$handle];

			if( $dep->deps ) {
				// This dependency has more dependencies! Do a recursion
				$urls[] = sg_walk_dependencies( $dep, $is_script );
			} elseif( false !== $dep->src ) {
				// Store URL of dependency
				$urls[] = sg_format_asset_url( $dep->src, $dep->ver );
			}
		}
	}

	// Store asset after its dependencies
	if( false !== $asset->src ) {
		// Add inline scripts/styles
		if ( $asset->extra ) {

			$inline_script = array_key_exists( 'data', $asset->extra ) ? $asset->extra['data'] : '';
			$inline_script = array_key_exists( 'after', $asset->extra ) ? implode( '', $asset->extra['after'] ) : '';
			$inline_script = trim( $inline_script );

			if ( $inline_script ) {
				if ( $is_script ) {
					$urls[] = '<script type="text/javascript" id="' . $asset->handle . '-js-after">
	' . $inline_script . '
	</script>';
				} else {
					$urls[] = '<style type="text/css" id="' . $asset->handle . '-inline-css">
	' . $inline_script . '
	</style>';
				}
			}
		}

		// Store URL
		if ( $asset->src ) {
			$urls[] = sg_format_asset_url( $asset->src, $asset->ver );
		}
	}

	return $urls;
}

function sg_format_dependencies( $enqueued_assets ) {
	// Flatten the array:
	// 1. Recursively iterate the array iterator
	$output_array_obj = new RecursiveIteratorIterator(
		new RecursiveArrayIterator( $enqueued_assets ) );

	// 2. Copy the iterator into an array
	$enqueued_assets = iterator_to_array( $output_array_obj, false );

	// Clean up duplicate assets
	$enqueued_assets = array_unique( $enqueued_assets );

	return $enqueued_assets;
}

function sg_list_scripts() {

	global $wp_scripts;
	global $enqueued_scripts;

	$enqueued_scripts = array();
	foreach( $wp_scripts->queue as $handle ) {
		$enqueued_scripts[] = sg_walk_dependencies( $wp_scripts->registered[$handle], true );

		//$enqueued_scripts[] = print_r( $wp_scripts->registered[$handle], true);
	}

	$enqueued_scripts = sg_format_dependencies( $enqueued_scripts );
}
add_action( 'wp_print_scripts', 'sg_list_scripts' );

function sg_list_styles() {

	global $wp_styles;
	global $enqueued_styles;

	$enqueued_styles = array();
	foreach( $wp_styles->queue as $handle ) {
		$enqueued_styles[] = sg_walk_dependencies( $wp_styles->registered[$handle], false );

		//$enqueued_styles[] = print_r( $wp_styles->registered[$handle], true);
	}

	$enqueued_styles = sg_format_dependencies( $enqueued_styles );
}
add_action( 'wp_print_styles', 'sg_list_styles' );

add_action( 'wp_head', function() {
	global $enqueued_scripts;
	echo '<pre>';
	echo esc_html( print_r( $enqueued_scripts, true ) );
	echo '</pre>';
	global $enqueued_styles;
	echo '<pre>';
	echo esc_html( print_r( $enqueued_styles, true ) );
	echo '</pre>';
} );