First, in the in-text citation, use locations instead of page numbers. For example:

Franklin (2009) asserted “there is a significant difference between knowing a thing because you have worked it out from the evidence, and knowing a thing because someone told you to believe it” (loc. 1799-1816).

Then, in the references section, mentioned that this is the kindle edition of the book:

Franklin, R. 2009. Unknown Knowns: Why we fail to question our own certainty. (Kindle Edition). Oxford: Oxford University Press.