Yes, there are a few blogs written by professional speechwriters. I’ll list eight of them by their author’s names in alphabetical order, along with a sample post.
[Dr.] Sam Cooper just uses his name. He has a post on February 4, 2019 titled Daniel Kahneman’s Thinking, Fast and Slow: a treasure trove of tips for speechwriters and speakers.
Charles Fleming has a blog titled Expression/Impression. He has a post on October 11, 2021 titled Keynote speeches: tips from politicians.
Patricia Fripp uses her last name for her web site and blog. On May 26, 2023 she has a post titled The best way to craft and deliver an engaging speech about yourself.
Brian Jenner has a blog titled The Speechwriter. He has a post on October 28, 2022 titled My ten favourite insights into writing. Brian also founded the European Speechwriter Network.
Nick Morgan has a web site titled Public Words, with a blog. On May 2, 2023 there is a blog post titled How to write an unforgettable speech.
David Murray has a blog titled Writing Boots, and subtitled On communication, professional and otherwise. His web site is ProRhetoric; David runs the Professional Speechwriters Association and edits the magazine Vital Speeches of the Day. He has a post on July 22, 2015 titled What makes great speeches: serious and charming people who tackle important questions with utter conviction. (Right?)
Eddie Rice has a web site called Rice Speechwriting, with a blog. There is a post on June 2, 2022 titled Honoring others: 7 prompts for what to say for rank promotions, awards, and ceremonies.
Anthony Trendl has a web site titled American Speechwriter with a blog titled Looking Up from the Typewriter. He has a post on March 16, 2023 titled Speech Tip: Danger, Will Robinson! Danger! (Speeches Aren’t Safe).
Back on July 20, 2010 there is an article by Cynthia J. Sparks at ProRhetoric titled Speechwriters who blog tell exactly why they do it.
The cartoon of a speechwriter was adapted from one at Wikimedia Commons.