Sittin’ On The Dock Of The Bay is a lovely song with a simple melody, but complex embellishments.
I have transcribed this version without many of the embellishments for a beginner student.
Setting the music out in Solfa allows the student to appreciate the structure of the melody. I would not recommend singing this through completely in Solfa, although you could if you wanted to. In this piece the Solfa is best used to practise small sections that the student is finding difficult.