mov ax,55

mov bx,10       ;bx -> divide by 10
DIV Bl        ;divide. AL is quotient, AH is Remainder

add al,48       ;any number + 48 = the same number in ASCII
add ah, 48
push ax  ;push ax to the stack

mov ah,0x0e  ;print to screen
mov bx,0x0007
int 0x10

pop ax     ;pop ax back from the stack
mov al,ah        ;puts ah into al to print with int 0x10

mov ah,0x0e      ;print to screen
mov bx,0x0007
int 0x10
    

hi, i use this code to print AX value, but it can't be greater than 99.....

mov ax,9999h

@@:
and al,0fh
add al,'0'
<print>
shr ax,4
jmp @b
    

Just in case this is not obvious for the OP the code above has several problems:
1. It will print trailing zeroes forever (unless <print> takes care of jumping out of the loop)
2. Ignoring problem 1., it will print only half of the digits of the numbers correctly, the other digits will always be printed as zero.
3. Assumes the numbers are in packed BCD form.
4. As already stated by the author, it prints the digits in the wrong order.

mov ax,9999h
mov bp,4
@@:
push ax
and al,0fh
add al,'0'
<print>
pop ax
shr ax,4
dec bp
jnz @b
    

mov ax,[sum]
mov bx,strsum

inttostr:
        ;In bx the offset to the target string
        ;In ax the unsigned integer to convert to string
        ;It converts an unsigned integer to an ascii string
        push ax
        push bx
        push cx
        push dx
        push si
        xor     cx,     cx
        ;xor     dx,     dx  THIS LINE IS BUGGY.
        mov     si,     10
label2:
        ;I divide the number by 10 repeatedly
        ; and I put the remainders in the stack.
        cmp     ax,     10
        jb      label1
        ;THIS IS THE PLACE FOR xor dx, dx
        ;CLEAR THE PREVIOUS REMAINDER.
        xor      dx,      dx
        div     si
        push    dx
        inc     cx
        jmp     label2

label1:
        push    ax
        inc     cx
label3:
        ;I retrive the numbers in the stack and
        ;I add to them the ascii value for '0' (character).
        pop     dx
        add     dx, '0'
        mov     byte [ds:bx], dl
        inc     bx
        dec     cx
        jnz     label3
        ;The service 9h of the 21h interrupt prints a string
        ;terminated by the character '$'
        mov     byte [ds:bx], '$'
    

Code:

        ....
        mov     byte [ds:bx], dl
        ....
        ....
        ....
        mov     byte [ds:bx], '$'
    

          ; print EAX
DECOUT:   mov     di, ASCII
          mov     cl, 0Ah             ; 10 decimal ASCII
          mov     ebx, 1000000000
P1:       xor     edx, edx
          div     ebx
          add     al, 30h
          mov     esi, edx
          mov     [di], al
          inc     di
          mov     eax, ebx
          mov     ebx, 0Ah
          xor     edx, edx
          div     ebx
          mov     ebx, eax
          mov     eax, esi
          dec     cl
          jnz P1
;-------
          mov     si, ASCII-1
          mov     dx, si
          inc     dx
ZERO:     inc     si
          cmp    BYTE[si], "0"
          jz  ZERO
          sub     si, 0Ah
          cmp     si, dx
          jz  short SKIP
          add     si, 0Ah
          mov     dx, si
SKIP:     mov     ah, 9
          int   21h
          ret

ASCII     DB "0000000000", "$"