" Is that 100% or 0%?"
Do not enter a percentage in that screen; it is a dollar amount that you would enter.
You should be able to determine whether capital gains are required to be distributed to the beneficiary(ies), are never distributed to the beneficiary(ies), of if you, as trustee, have discretion to distribute capital gains from the language in the trust instrument.
Typically, capital gains remain with the trust, are considered part of the corpus (trust assets), and the trust pays any income tax due on the gains, except in the final year of the trust when all assets are distributed.
In many instances, however, the trustee either has the discretion or is required to distribute capital gains to the beneficiary and you would enter the amount to be distributed in "capital gains attributable to income".
