Between "I have a good understanding of...", "I understand..." and "I know about...", which would be more appropriate to use for creating a likert scale survey questionnaire?
I think it depends on how familiar your respondents will be with the items. For example, if almost everyone is at least familiar with the content, then a stronger statement such as, "I have a good understanding of..." would be more appropriate.
Otherwise you might consider something like, "How familiar are you with..." ranging from Have Not Heard Of to Very Familiar.