In default setting, category slug is not displayed on single post.
To override this behaviour, add following snippet into your theme functions.
Appearace > Editor > functions.php
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Hi everyone Dahz support will be offline through the weekend
We will be back to assist you on Monday
Please note that our support is available on Monday - Friday from 9 am to 5 pm (GMT +7).
Sorry for the inconvenience. Happy weekend!