"Jsem odborníkem na všechno."

Translation: I am an expert on everything.

[jtd742]

"I am an expert at everything" feels more "correct" to me than "on" somehow

[svrsheque]

your feelings may be in a minority.

[JohnBraga1]

and insufferable with it

[Jakub72S]

why: expert on something (on as location) and not: expert for something??

[Steve254604]

For example:

“I am an expert on these companies”: I have studied them for years and know how they work.

“I am an expert for these companies”: I work for them, they employ me, or they have hired me to be their expert (e.g., in court, or as a consultant).

I also agree with joedoolz47 regarding the use of “at” in certain cases. For example: “I am an expert at tennis” (seems to suggest that I play it very well) vs. “I am an expert on tennis” (suggesting I have studied the history or mechanics of the game).

You could also use “in”, e.g., for a field of study. For example: “I am an expert in (the field of) Medieval literature” vs. “I am an expert on [X, Y, or Z particular manuscript].”

[Tibro3]

Yup. There needs to be more flexibility/wider acceptance of possible answers here.

[Holandsky_Honza]

Why do we use 'odborníkem' here and not 'odborník'?

[VladaFu]

Nominative is also possible. Instrumental is better for temporary things or things you can become. But it is quite blurry https://cs.wikipedia.org/wiki/Nominativ#Konkurence_nominativu_a_instrument%C3%A1lu

[Adrian198829]

Best sentence ever in DL because of a personal memory :) When my youngest daughter was 8-9 years old, she saw me giving someone a business card and asked me what it was and developed hers on her own. Martina Alvarez Garcia, expert on almost everything :) I asked her if she was an expert on everything and she said that no, that she was too young, but that she knew a lot, thus, almost. I framed that business card and I still have it :) You made my day with this memory :) thanks a lot! And thanks a lot for all your work! I know that we ask too many questions and are grateful for all the effort you put. By the way, many times I am amazed by your expert knowledge of the language and its history. I can assure you that I don't have that knowledge of my own language!

[Eri168273]

It says I have a typo and suggests the correction "Im an expert on everything." Doesn't look correct to me.

[BoneheadBass]

We can't tell you why the apostrophe was left of an apparent "correction," because Duolingo controls that. And because we don't know what you wrote, since we have no current report, we can't tell you why you got the proposed correction.