You're missing a closing parenthesis from the double line (last printf).
Also, it's not an error, but a warning: the correct type to print for the return type of sizeof() is a long unsigned int (lu), not a signed int (d).
Last, but not least, sizeof() works on types as well, not just on variables.
#include<stdio.h>
int main()
{
char ch = 9;
int inum = 1052;
double dnum = 3.1415;
printf("ch의 크기: %lu\n", sizeof(ch));
printf("inum의 크기: %lu\n", sizeof(inum));
printf("dnum의 크기: %lu\n", sizeof(dnum));
printf("char의 크기: %lu\n", sizeof(char));
printf("int의 크기: %lu\n", sizeof(int));
printf("long의 크기: %lu\n", sizeof(long));
printf("long long 의 크기: %lu\n", sizeof(long long));
printf("float의 크기: %lu\n", sizeof(float));
printf("double의 크기: %lu\n", sizeof(double));
printf("printf works on types too! sizeof(char) = %lu\n", sizeof(char));
return 0;
}