According to the instructions
for the 1120S K-1, it is Box 8a on the K-1 that should flow to
Schedule D, line 12.
Box 8a. Net Long-Term Capital Gain (Loss)
Report the net
long-term capital gain (loss) on Schedule D (Form 1040), line 12.
Box 10, Code E should flow to line 10 of Schedule D.