Try this:
$query = new WP_Query( array(
'meta_query' => array(
'relation' => 'OR',
'resume_skills_clause' => array(
'key' => '_resume_skills',
'value' => $_GET['resume_search_keyword'],
'compare' => 'LIKE'
),
'resume_job_duties_clause' => array(
'key' => "_resume_job_duties",
'value' => $_GET['resume_search_keyword'],
'compare' => 'LIKE'
)
)
));