If you are tax resident in Kenya, your business income, employment income and consultancy income from BOTH Kenya and a foreign country is ALL taxable in Kenya, regardless of whether that income has already been taxed outside Kenya.
If Kenya and the foreign country have signed a double tax agreement between them, then the Kenya Revenue Authority will recognise the foreign tax paid in the foreign country, in determining whether any further tax is due in Kenya for your worldwide business, employment or consultancy income.
This means that where income is earned in a foreign country that Kenya does not have a double tax agreement with Kenya, then that income may be taxed twice, as tax on such foreign income will not be recognised by KRA.