This means that you need to know more about how employees are taxed in Thailand and the only way to gain this knowledge is through reading.
After you get your first salary in Thailand, you should obtain a tax ID within 60 days. This is because any income from Thailand employment is subject to Thai tax laws immaterial where the employment income is paid. Income can be in the form of salary, wages, bonus, allowance, gratuity, pension, commission, education payment, house rent allowance, utility bills, etc. Even profits gained from business, commerce, and trade are subject to taxes whether or not you are resident of Thailand.
However, you should not let this deter you because you could be entitled to tax exemptions. Business expenses, transport expenses, costs incurred, gifts, insurances and taking care of dependents are exempt from taxes. You can also make a contribution to a social security fund but not over 3 percent of your wages and it should not exceed more than 15,000 baht per month.
If you are resident of Thailand, you also have pay tax on investment income and capital gains derived from sources from outside Thailand if the investment income and capital gainsre are remitted into Thailand. However, a non-resident does not have to pay tax on investment income and capital gains from outside Thailand. The good news is that you will not have to pay tax on capital gains on the Stock Exchange.
If you are resident of a country that has a double taxation agreement with Thailand, you may end up getting exemption from Thai personal income tax.