As character names:

U+0308 COMBINING DIAERESIS character (̈)

As raw characters:

̈

As a string of HTML entities:

̈

Decoder output:

Byte number 1 is decimal 204, hex 0xCC, octal \314, binary 11001100
This is the first byte of a 2 byte sequence.

Byte number 2 is decimal 136, hex 0x88, octal \210, binary 10001000
This is continuation byte 1, expecting 0 more.

U+0308	COMBINING DIAERESIS
	= double dot above, umlaut
	= Greek dialytika
	= double derivative
	x (diaeresis - 00A8)