A testimonial is a formal statement testifying to your book’s value and indirectly, your qualifications as an author. Whether you include them in your book or on your landing page, testimonials are powerful influencers that literally sing your book’s praises.
If you plan on including testimonials in your book, you should try to gather them together BEFORE your book is published. Otherwise, you need to add them later and upload your manuscript again.
You could request a testimonial from other writers who have read your book or experts on the topic your book focuses on. Look for endorsements from someone that inspires confidence in you or your book. So although your mom would love to write a testimonial, unless she is an expert in her field, maybe pass.
Asking for a testimonial doesn’t have to be difficult. Begin your request with flattery because it will get you everywhere. Explain how this person or his or her work inspired you, changed your life, or means the world to you. Be sure to state that if this person needs a testimonial for a book or endorsement for a business, that you would be happy to reciprocate in this manner.
Then tell this person exactly what you are requesting from them which is a few lines about your book before a not too distant but not too imminent date.
Finally, ask how he or she would like their name and credentials listed. Offer to include a link to a business or website. If someone prefers to remain anonymous, clarify if using their initials or a pseudonym would be acceptable.

Amazon has a Look Inside feature which could highlight those testimonials very well if you decide to have a testimonial page included in your book. If you do, place them as close to the beginning of the book as you can get since Amazon only shows the first few pages.
Amazon also allows you to add testimonials to the book’s landing page via your Author Central page and they appear on the book’s landing page on Amazon. This is much simpler to update since you aren’t constantly uploading your manuscript for each new testimonial. However, you’ll need to decide where your testimonials would work best for you.
Don’t go overboard with the number of testimonials you use. A page and a half of praises are probably sufficient. If you have more than that, consider including some in your book and others on your landing page so that readers aren’t overwhelmed with your greatness.
Assignment: Gather testimonials to include either in your book or on your book’s landing page.