[org 0x0100]

n1: db 1
n2: db 2
largest: db 0
    mov ax, byte[n1]
    mov bx, byte[n2]
    cmp ax,bx
    jg next
    mov [largest],bx
    jmp endrtn
next:mov [largest],ax
endrtn: 
        mov ax, 0x4c00
        int 0x21 

error in line 6 and 7 error is mismatch in operand sizes

rproffitt commented: Example. Yes, a fine example of how to not get help. -3

Also, error behind your keyboard.