forex dif le..
i ask tax agent bfore , they say taxable wor..

Capital gain is tax exempted. So if you gain on forex by investment then it is considered capital gain.
All income are considered taxable unless stated otherwise or one can prove the allowances are essential to carry out your job then only can be waived.

Inland revenue board will query why the person wire-transfer you in the first place. Not as simple as that.

For capital gain, you need to keep properly your transaction documentation, slips, contract noted or any other documentation proof that show you are actually gain money through capital appreciation.