Thanks for reporting. Just to let you guys know, this is not an error of the course creators. Something fishy is clearly going on in the engine compartment. I took this lesson a bunch of times today, and encountered the following puzzling behavior of this sentence:

• When the sentence is presented as a listening exercise (where you write what you hear in Czech), the "Translation" is displayed as Where is my parents' car?
• When you are asked to translate from Czech and enter Where is my parents' car?, you are warned that your answer has a typo, and the translation shown under that warning is Where is my parents car? with the word parents underlined.
• When you are asked to translate from Czech and enter Where is my parent's car? or Where is my parent car?, the answer is rejected as "You used the wrong word.", and the translation shown under that message is Where is my parents' car? with the word parents' underlined.
• When you are asked to translate from Czech and enter Where is my parents car?, the answer is accepted without a warning.
• When you are asked to translate from Czech and enter random garbage, the answer is rejected, and the "Correct solution" shown in the rejection is Where is my parents' car?

As a mere human, I am not be able to determine what Duolingo thinks the correct answer is. Looking inside our exercise configuration shows the following:

• Where is my parents' car? is the main translation.
• Where is my parents' automobile? and Where is the [car/automobile] of my parents? are the side translations.

All I can do is request that this behavior be fixed or explained.

I noted an issue with a similar translation, but there's a problem with this one too. I translated this as 'Where is my parents' car?' and the answer key said that I had a typo and it should have been 'Where is my parents car?' This is incorrect, the apostrophe should be there.