Caller out to engage occasionally good Swiss singer? (8)
I believe the answer is:
yodeller
'swiss singer?' is the definition.
'yodeller' can be an answer for 'singer?' (yodeller is a kind of singer). I am unsure of the 'swiss' bit.
'caller out to engage occasionally good' is the wordplay.
'caller out' becomes 'yeller' (I can't explain this - if you can you should give a lot more credence to this answer).
'to engage' indicates putting letters inside (some letters get engaged in others).
'occasionally' means one should take alternating letters (letters taken at regular intervals or occasions).
The alternating letters of 'good' are 'od'.
'yeller' going around 'od' is 'YODELLER'.
Can you help me to learn more?
(Other definitions for yodeller that I've seen before include "Alpine singer" , "Vocalist" , "Singer using falsetto" , "Mountain air for him" .)