Oohkay I was confused about that. Now Im finally getting working code and the messagebox comes up but there's no message text! So close!
If I'm keeping each digit as a quad-word then I need to add 8*the number of digits to rdi, right? And I believe forgot to compensate for the 00 end of string.
mov rdi, Jer ;move address of Jer to rdi
add rdi,56 ; 7 digits (including 00) * 8 (quadword) = 56
mov qword rsi, 0 ;load 0 into the source
mov qword [rdi],rsi ;manually moving instead of movsq
sub rdi,8 ;move rdi back 8 places
mov dword ecx,10
xor rdx,rdx ; clear rdx for division
div ecx ; divide by 10
movsxd rdx,edx ; store digit onto rdx
add rdx,48 ;convert to ascii
mov qword rsi,rdx ;load digit into source
mov qword [rdi],rsi ;instead of movsq
sub rdi,8 ;move rdi back more places
mov rdx, Jer ; Not sure if I'm supposed to be moving the address or the contents, but I tried both