How to pass a more variable with page/subpage in Wordprees URL?

function add_custom_query_var( $vars ){ 
$vars[] = "q"; 
return $vars; 
} 
add_filter( 'query_vars', 'add_custom_query_var' );

mydomain/how-we-work/our-process/?q=more-value

You can handle it with

get_query_var( 'q' );

Edit1:
If you want to use with ‘SEO URL’ you need to add_rewrite_rule
function add_rewrites(){
add_rewrite_rule(
‘^how-we-work/our-process/([^/]*)/?’,
‘index.php?pagename=how-we-work/our-process&q=$matches[2]’,
‘top’
);
}
add_action( ‘init’, ‘add_rewrites’ );