How do i display zip code options during checkout [closed]

The postcode field was hidden for Nigeria in 3.5, you can see the reasoning given here: https://github.com/woocommerce/woocommerce/issues/21055

While the Nigeria Postal Service (http://nipost.gov.ng/) introduced
Postal Codes a few years ago, they aren’t being used by hardly anyone.

Nobody knows their postal codes as the implementation is very
convoluted and nothing was done to sensitize the public or encourage
their use. You won’t find them on any addresses and they aren’t
required for finding a building/location or for delivering parcels.

If this is incorrect, you should file an issue.

To change this behaviour on one site, though, you can use filter woocommerce_get_country_locale, like so:

add_filter(
    'woocommerce_get_country_locale',
    function( $locales ) {
        $locales['NG']['postcode']['hidden'] = false;

        return $locales;
    }
);