Within the Sales Document edit screen, the notes dialog has spellcheck functionality. However, in the the Interaction tab, the notes in that dialog there does not have this functionality.
Official response
Product Development
This is now available in SalesPad 5.6.8!
Relevant release notes:
ADDED: Interaction Entry: The Notes and Subject fields now provide spellcheck functionality.
Thank you for this idea! I have created an internal case for further review.