I want to connect the sense hat to a raspberry using jumping wires. I understand that I need to connect the highlighted pins in this schema of the pin out.
One of the reasons that I am unsure about this, is because the ground wires are a sort of highlighted in the linked pin out schema, but not completely like the other required pins..
Whenever you connect a Pi GPIO to an external device you also need to connect a Pi ground to that device (you can connect more than one to that device if you want but it is not usually needed).
The blurb includes Needs 5v and 3v3 power.
That means you also need to connect the 5V and 3V3 power pins.
Yes. Bus connections require a common ground because they require a common voltage, and since inevitably the circuit on both sides are electrically powered, any connection between them requires a common ground.
In this case the hat is being powered by the pi and a 3.3V and 5V pin are indicated, as are the grounds, which may imply that they are all also connected on the hat -- but you only require one since it is very very unlikely there are independent circuits on the board.
