Answer:
(1) Kennen
(2) Wissen
(3) Kennen
(4) Wisst
(5) gewusst
(6) Kennen; kennt
(7) Weißt
Explanation:
The difference between <em>kennen</em> and <em>wissen</em> is tricky for English-L1 learners because they can both translate to the same "to know." (Interestingly, for native German speakers, they are semantically clearly delineated and there is absolute no confusion about when to use which.)
There are many websites listing hints on when to use which, but I find the following most useful:
Kennen: if you can replace it with "recognize" then it is likely a candidate for "kennen." For example, the first sentence in your problem "Do you know the saying?" --> "Do you <em>recognize</em> the saying?" (hence, use "kennen")
Wissen: you have "knowledge about something" For example, in the first sentence of your problem, if you plug in "Do you have knowledge about the saying" - that sounds clumsy, so "wissen" is not a good candidate (in contrast to the "recognize/kennen" test). But for sentence #2: "(do you have knowledge about) how many people live in Germany" - that sounds like a good fit, and "wissen" is appropriate.
Eventually, with practice you will be able to distinguish the two appropriately and quickly.
