Can I only eat it in Hat Yai?
No. Hat Yai-style fried chicken is sold in other regions too. If you have come to Hat Yai, try the dish known by the name of the city with sticky rice.
Hat Yai Fried Chicken · ไก่ทอดหาดใหญ่
In Hat Yai, try crispy fried chicken served with fried shallots. It is Hat Yai fried chicken, known by the name of the city. The shallots add a savory taste and aroma to the crispy texture of the chicken, and it goes well with sticky rice. Put a little of the shallots served alongside on top of the chicken and take a bite.

It is a dish where you enjoy the crunch of fried chicken together with the savory taste of shallots. Another feature is that it is seasoned with aromatic ingredients such as garlic, coriander root and white pepper. Before you add the sauce, try the chicken and shallots together on their own.
Eating the fried shallots together with the chicken brings out more of the savory taste.
Hat Yai is a city in the Songkhla area, where the food culture of Chinese and Muslim communities sits side by side. Hat Yai fried chicken is known as a signature dish of this area. It is sold in other cities too, but if you have come to Hat Yai, have it with sticky rice as a meal.
No. Hat Yai-style fried chicken is sold in other regions too. If you have come to Hat Yai, try the dish known by the name of the city with sticky rice.
No. You cannot decide whether something is halal from the kind of meat alone. If you need a halal meal, check the restaurant's certification together with the actual ingredients and cooking conditions.
If you want to read more about the food and the regions behind it, these sources are a good next step. Ingredients and cooking methods can differ from one place to the next.