Those look like the "knees" on a bald cypress.  If this is definitely a Dawn Redwood, this rooting is probably due to the roots unable to grow properly in the soil.   This could be due to hardpan soil, high water table, or maybe the soil was compacted with the tree spade.  Trimming roots is not a good idea, but to get the best answer about if and how many roots can be damaged, a certified arborist is the best to ask.  https://ohiochapterisa.org/aws/OCISA/pt/sp/trees4ohio_find-an-arborist