Gender: boy
School:
School #20B
@Sonya_6 - According to the SOURCE INFORMATION NOTES, PRZ do M + No. means "Moved to moved to apt. no. in same house" AND PRZ dom + No. means "Moved to other house in same street." So, on December 20, 1942, Aleksander probably moved from one address to another. I hope this helps.
I should have also noted that for Aleksander, the NOTE refers to PRZ DOM 2 before the date. This suggests that he moved into apartment #2. Though it is unclear at which of the two street addresses he made this change.