Ordinarily, if you are the beneficiary of a trust, you would receive a K-1 Form 1041 to report income from that trust. If the property was sold but you did not get a distribution, then it is not reportable by you.
A trust is supposed to file K-1 Form 1041 if it has gross income of $600 or more.
If you are the sole beneficiary of the trust, then for tax purposes, the trustee attorney is correct, assuming you received the distribution. It's just cleaner if you have the K-1. If you had the K-1, you would report the capital gain that way; without, you are left to file it on your Schedule D. Record the transaction as you would report the sale of a security, using Code F for the Sale Category.