The phrase "almost everything I know" is correct and usable in written English.
You can use it when discussing the extent of your knowledge on a particular subject or topic, often implying that there are some exceptions or limitations to that knowledge.
Example: "In terms of programming languages, almost everything I know comes from online courses and tutorials."
Alternatives: "nearly all that I know" or "most of what I know".
"Ed Rollins has taught me almost everything I know," he said.
Instead I acquired almost everything I know about language in Latin classes – and wasn't I lucky to have them?
Let me be upfront: Almost everything I know about Bellow that I didn't guess from reading him, I got from the encyclopedic Atlas.
Gareth Young is a local government officer and the co-author and presenter of the popular welovelocalgovernment blog and podcast By Kersten England I learnt almost everything I know about being a corporate parent from an extraordinary young woman I met courtesy of Radio 4.
An admission: almost everything I know about Griffiths, and Huggins, and the 1850s pioneers of women's footy, and the women who played during both world wars to raise money for the troops, I know because of Play On! – a new history of women's football written by Brunette Lenkić and Rob Hess and published late in 2016, right as a million people were tuning in to the AFLW all-stars match.
"He taught me everything or almost everything I know about golf, and I would have loved him to see me turning pro.
"It's where I learned almost everything I now know.
Having consulted dozens of authorities on snail farming, most of whom disagree about almost everything, I do know I will have to clean them, inside and out.
As I researched my screenplay, I realised that almost everything I thought I knew about Lawrence was wrong.
Some exhibitions pale in the memory, but this one -- put together by the combined forces of the Met, the Tate, and the Prado -- still grips me, and its alchemical mix of biography, imagination, and paint really did make me reconsider almost everything I thought I knew about art and how it communicates human intelligence.
Yes, there's a body of knowledge you should have before you start taking massive action (and you can click here to get the resource sheet that taught me almost everything I came to know about marketing initially).
