In C and C++, NULL, 0 and '\0' are all the same. In Java, 0 and '\0' are the same but null is something completely different; it has no ASCII value because ASCII values are only available for chars. null is not a char.
I presume you mean to ask what the "null character" (as it is called in ASCII) looks like when you print it out. It doesn't look like anything. Try this
And you won't see anything.