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In Woocommerce, I use following block of code that adds a custom fee in cart and checkout, based on total weight for a specific country:

function weight_add_cart_fee() 

 // Set here your percentage
 $percentage = 0.17;

 if ( is_admin() && ! defined( 'DOING_AJAX' ) )
 return;

 // Get weight of all items in the cart
 $cart_weight = WC()->cart->get_cart_contents_weight();

 // calculate the fee amount
 $fee = $cart_weight * $percentage;

 // If weight amount is not null, adds the fee calcualtion to cart

 global $woocommerce;
 $country = $woocommerce->customer->get_country();
 if ( !empty( $cart_weight ) && $country == 'SK' ) 
 WC()->cart->add_fee( __('Recyklačný poplatok (podľa váhy): ', 'my_theme_slug'), $fee, false );
 

add_action( 'woocommerce_cart_calculate_fees','weight_add_cart_fee' );

But I need to make this fee taxable. How to make it taxable?.

There is some mistakes and your code is outadated. Try the following instead (with a taxable fee):

add_action( 'woocommerce_cart_calculate_fees','add_fee_weight_based', 10 , 1 );
function add_fee_weight_based( $cart ) 
 if ( is_admin() && ! defined( 'DOING_AJAX' ) )
 return;

 $percentage = 0.17; // Percentage
 $targeted_country = 'SK'; // Country
 $cart_weight = $cart->get_cart_contents_weight(); // Total weight


 if ( $cart_weight > 0 && WC()->customer->get_shipping_country() == $targeted_country ) 
 $cart->add_fee( __('Recyklačný poplatok (podľa váhy): ', 'my_theme_slug'), ($cart_weight * $percentage), true );
 

Code goes in function.php file of your active child theme (or active theme). Tested and works.

Make a fee taxable

To make a fee taxable, in the WC_Cart add_fee() method, you need to set the 3rd argument to true (taxable)…

The 4th optional argument is related to the tax class that you can specify if you need to set a specific tax class