A lot of people asked this question when they transfer their H1B visa under AC21. I am currently in the same process as well. I did some research and found there is no SOC Code field in I-129 (H1B) application. Job title and Nontechnical Job Deion are the only related items listed in this form under Part5.
SOC Code is a classification for the job category, which is used in I-140 form only based on my knowledge. I am thinking often times that your new employer attorney asks this information is just trying to figure out to write a more meaningful job deion and company support letter to make sure this transfer has no\less impact with your I-485 application.
Disclaimer: this is just my personal opinion. I am not a lawyer.
SOC Code is a classification for the job category, which is used in I-140 form only based on my knowledge. I am thinking often times that your new employer attorney asks this information is just trying to figure out to write a more meaningful job deion and company support letter to make sure this transfer has no\less impact with your I-485 application.
Disclaimer: this is just my personal opinion. I am not a lawyer.