The current sensing resistors should be about 1000 times smaller than the series resistors so R7 should be 0.1 ohms if R1 is 100 ohms. The power dissipated in the current sensing resistors will be small so any style may be used. Note that these current sense values give four ranges from 100mA to 100uA with about 10 mV per vertical division for the oscilloscope. About 100k is fine for R5 and R6 although just about any fairly high values will work here. These resistors set the amplitude for the scope's horizontal input and may be left out entirely if the scope has good horizontal gain control.
Many scopes just have one or two gain settings and some sort of adjustment is necessary.
A silicon diode capable of handling the highest test current and voltage. A 1N4002 should work well for most applications. When the diode is in the circuit, it will limit the negative swing to under -1 volt. Here is a simple version with a single voltage range of about 18 volts peak and a current limit of about 18 milliamps peak. This one-range tracer is quite useful for quick checking of zeners, transistor junctions, LEDs, and most other semiconductors.