Q:

How will current divide in a LED matrix in one select line when there are 8 data lines?

simulate this circuit – Schematic created using CircuitLab
Let's say I have a select line that is connected to 8 data lines in an LED matrix. The current at the drain of the MOSFET is 800mA. Will the current divide among the 8 LEDs into 100mA for each data line? And if so, does that mean the current in the wire between the first and second diodes on the select line is 700mA, the second and third diodes 600mA, and so on?

A:

Yes, current will divide equally according to KCL assuming that each diode is ideally same. Remember that leds unprotected by resistors will try to consume as much power as it's available, potentially causing its damage.
Try out Paul Falstad's circuit simulator, it's incredibly useful tool.

