<?php
// See https://wordpress.stackexchange.com/a/301351/137402 for details.

add_action( 'init', 'my_register_questions_post_types' );
function my_register_questions_post_types() {
    register_post_type( 'science-question', array(
        'label' => 'Science Questions',
        'public' => true,
        'supports' => [ 'title', 'editor', 'custom-fields' ],
        'rewrite' => array(
            // The rewrite slug. You can change 'science' to whatever you like.
            'slug' => 'science/question/%task_id%',
        ),
        // Other args here.
    ) );

    register_post_type( 'math-question', array(
        'label' => 'Math Questions',
        'public' => true,
        'supports' => [ 'title', 'editor', 'custom-fields' ],
        'rewrite' => array(
            // The rewrite slug. You can change 'math' to whatever you like.
            'slug' => 'math/question/%task_id%',
        ),
        // Other args here.
    ) );
}

add_action( 'init', 'my_register_questions_taxonomies' );
function my_register_questions_taxonomies() {
    // Set the slug to 'task'.
    register_taxonomy( 'task', array( 'science-question', 'math-question' ), array(
        'label' => 'Tasks',
        'public' => true,
        'hierarchical' => true,
        // Other args here.
    ) );
}

add_action( 'init', 'my_register_questions_rewrite_tags' );
function my_register_questions_rewrite_tags() {
    add_rewrite_tag( '%task_id%', '(\d+)' );
}

// Replaces %task_id% in the permalink (i.e. $post_link).
add_filter( 'post_type_link', 'my_filter_questions_post_type_link', 10, 2 );
function my_filter_questions_post_type_link( $post_link, $post ) {
    if ( false !== strpos( $post_link, '%task_id%' ) ) {
        $cats = get_the_terms( $post, 'task' );
        $cat_id = 0;

        // If the post was assigned to at least one "task" category.
        if ( $cats && ! is_wp_error( $cats ) ) {
            $cat_id = $cats[0]->term_id;
        }
        // Else, /{SLUG}/question/0/{POST SLUG} should work well. =) But of
        // course, all "question" CPT posts should be assigned to *at least*
        // one "task".

        $post_link = str_replace( '%task_id%', $cat_id, $post_link );
    }

    return $post_link;
}