Foreign trust income is declared on a paper tax return SA1107, along with a paper SA100 or if you have a government gateway user ID and password, you can choose between submitting a paper tax return and buying a commercial tax return that supports trust income. You cannot use HMRC online tax return, as it does not support trust income. You can find a list of commercial suppliers at:
Self Assessment commercial software suppliers
You ar required to submit the tax return in its entirety in the same format.
The Self Assessment Tax Return is used to declare world-wide income, so your wife would declare her employment income, UK interest and dividends and foreign sources of income.
There are supplementary pages for self assessment that cover, employment, self employment, partnerships, income from property, foreign income and gains, UK and foreign trusts, capital gains and residence.
The money you earn from the Hong Kong stock market is likely to be a capital gain. This would be reported on SA108 and if foreign tax paid, SA106.