Can I only eat it in Hat Yai?
No. Other areas sell Hat Yai-style fried chicken as well. If you are in Hat Yai, it is a good idea to 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, a dish known by the name of the city. The crispy chicken gets the savory aroma of shallots, and it goes well with sticky rice. Put a little of the shallots that come with it on top of the chicken and take a bite.

You enjoy the crispness of the fried chicken and the savory flavor of the shallots together. It is also characterized by seasoning with aromatics such as garlic, coriander root and white pepper. You can eat just the chicken and shallots before you add any sauce.
Eat the fried shallots together with the chicken for more savory flavor.
Hat Yai is a city of 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 are in Hat Yai, have it as a meal with sticky rice.
No. Other areas sell Hat Yai-style fried chicken as well. If you are in Hat Yai, it is a good idea to try the dish known by the name of the city with sticky rice.
No. You cannot tell from the type of meat whether a dish is halal. If you need a halal meal, check the restaurant's certification and 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 place to start. Ingredients and recipes can vary from one restaurant to the next.