Housing stipends are taxable income. If you use money for housing it is taxed just like your other income is. So whether you used the $20k for rent or to go on a cruise, the tax treatment would be the same. If your ONLY income is that $20k, and you are single, then you would have $5,400 in taxable income after subtracting your standard deduction of $14,600. The tax on that would be around $540 as you would be in the 10% tax bracket.
How did you enter the stipend? Is it being treated as self-employment income? Do you have any other income?
If you are paying taxes on the income in another country, you my be able to claim the foreign tax credit.