You can use the wp_trim_excerpt() to get the excerpt of the content.
You can use it inside your loop to get the excerpt of each post
the string provided to a maximum of 55 words if it is more then a […] will be added to the end of the string.
<?php
$recent_posts = wp_get_recent_posts(array('post_type'=>'jokes'));
foreach( $recent_posts as $recent ){
echo '<li><a href="' . get_permalink($recent["ID"]) . '" title="Look '.esc_attr($recent["post_title"]).'" >' . $recent["post_title"].'</a> </li> ';
$excerpt = wp_trim_excerpt( $recent['post_content']); // $excerpt contains the excerpt of the concerned post
echo $excerpt;
}
?>