How can I; Serial.println() a binary output that will give all the leading zero's of a variable?

[J-M-L]

try this

void printBin(byte aByte) {
  for (int8_t aBit = 7; aBit >= 0; aBit--)
    Serial.write(bitRead(aByte, aBit) ? '1' : '0');
}
void setup() {
  Serial.begin(115200); Serial.println();
  byte x = 0b00001100;
  printBin(x);
}

void loop() {}