Get the permalink for a blog post from any site on the network. This function is the same as get_permalink(), except that you can get the permalink for a post from any blog on the network, not just the current blog.
<?php echo get_blog_permalink( $blog_id, $post_id ); ?>
From any blog in the network, get the permalink for post with ID 6 on blog ID 3.
<?php echo get_blog_permalink( 3, 6 ); ?>
get_blog_permalink() is located in wp-includes/ms-functions.php
.