Hide ticket field based on custom field from contact

Hi, I have added custom checkbox to my Contacts and I want to hide my custom drodpown box based on value of that checkbox. I don’t know how to access custom fields of contact on new ticket page with liquid. I found one solution saying that I’m able to get custom fields like this “portal.user.cf_nameOfYourCustomFields” but its empty. Here is a snippet of my code

jQuery(document).ready(function(){
{% if portal.user.cf_ukryj == false %}
jQuery('#helpdesk_ticket_custom_field_cf_umwm_2175734').hide();
{% endif %}
});

Any suggestions how to do that?