If you have utilized margin in your account to purchase securities, you should be able to see your outstanding margin balance under: Me > Live Account > Account Overview:
If the balances are showing in a negative amount, that represents your outstanding margin balance.
The margin annual interest rate for both USD and HKD can be found here.
Daily margin interest = Annual margin interest rate / 360 * Your overnight margin balance.
For example, your outstanding margin balance is: $10,000 and the annual margin interest is 5.08%; then your daily margin interest would be: 5.08%/360*10,000=$1.41
Margin interest is calculated and accumulated daily and deducted from your account on a monthly basis, usually on the 5th day of each month. For instance, the margin interest generated in March will be deducted from the account on April 5th.
When you liquidate your position or deposit new funds into your account, those funds will be used to cover your margin balances.