a.  

A blend of the initial CV (consonant and vowel) of what and the final C of which to form watch.

b.  

A substitution of tree for roof. Both are nouns and so either is syntactically okay in the context.

c.  

An exchange of the stems learn and need. Note that the suffixes (-er and -s) are stranded, i.e. remain in their place in the sentence frame.

d.  

A substitution of maid for music. Both maid and music can occur in expressions where they immediately follow that word.

e.  

An exchange of wine and dinner. Both are nouns that have been selected for output in the sentence but they are put into the wrong 'slot'.

f.  

An anticipation of the noun player which appears in the slot where the nounpeople should be. Note that player is made plural, matching the plural noun people. This error was self-corrected and is actually ambiguous as it could have been an interrupted exchange of player and people.

g.  

A perseveration of gym which appears both where it should be and in the position (as seen from the self-correction) of piscine.