Learn Dutch: Je kunt elke vierkante pixel goed zien. - You can see every square pixel well.

Pixel is a de word (de pixel). When modifying a de word, the determiner elk gets an -e added to it. If it were a het word, you would just use elk (for example, elk scherm).

Why does vierkant just get an -e without any other spelling changes, unlike some other adjectives?

The base adjective is vierkant (square). When we add the adjectival -e to make vierkante, the spelling of the root stays the same. Unlike words ending in a single consonant after a long vowel (where you drop a vowel, like groot becoming grote), vierkant ends in two consonants (-nt), so the spelling rules don't require any shifts to maintain the correct pronunciation.

Is it also correct to say Je kan instead of Je kunt?

Yes! For the pronoun je (or jij), both kan and kunt are completely correct. Je kan is slightly more informal and very common in spoken Dutch, while je kunt is standard in both writing and speech.

Why is the word order goed zien at the end, rather than putting goed right after the first verb?