This is a hard question because people use LingQ differently.
Some people mark everything as known, even if it’s an improperly parsed phrase or a repeated thing like “two, three, four, second, third, fourth, etc.” and in chinese “one X”, “two X”, “three X”, and “X” alone, where X is any of hundreds of measure words. This results in very high known word counts.
Others are more strict about it and their counts are much lower.
From what I’ve read, once you know the most common 3000 or so words, you can participate in most general daily conversations and pretty easily move through day-to-day life. Anything deeper will require domain-specific vocabulary. How long this takes depends on your target language and your native language, and how much time/effort you put in.
For example, native English speakers can probably get there in Spanish in a year if they work hard at it. I spent a day in Spain recently and was astonished how much Spanish an American just kind of knows with no effort. On the other hand, for a native English speaker Japanese, Chinese, etc. can take 2 or more years to get comfortable.
Hope that helps!