Since WordPress 4.7, these functions are available:
get_theme_file_uri() – if using a child theme, it will return the child theme’s full URI. Otherwise, it will return the main theme full URI.
e.g.
echo get_theme_file_uri(); // www.site.com/wp-content/themes/twentytwenty-child
It’s also possible to send a subfolder/file as parameter, like so:
echo get_theme_file_uri('images/logo.png');
// www.site.com/wp-content/themes/twentytwenty-child/images/logo.png
get_theme_file_path() – same as get_theme_file_uri() but will return the full path of the child theme or main theme.
echo get_theme_file_path(); // C:\wordpress/wp-content/themes/twentytwenty-child
For child theme usage, there are the following functions:get_parent_theme_file_uri()get_parent_theme_file_path()
Reference:
https://developer.wordpress.org/themes/basics/linking-theme-files-directories/#linking-to-theme-directories