Typically, dosages of 1-3g are used as a preventative treatment for nausea. This applies to morning sickness in pregnancy, motion sickness, and sometimes chemotherapy or operation-induced nausea.
For other usages of ginger, 1g is typically used. This seems to be effective for increasing intestinal motility, but was insufficient in reducing blood glucose in the one study attempting it.
For testosterone boosting, a supplement is probably advised. The dosage used in rats, after conversion to humans based on Body Surface Area, equates to about 14g from natural sources (usually less of an extract percentage than is possible with supplements).
Ginger can be ingested via several ways, and the following is an approximate standardization table for 1g of Ginger Extract:
A capsule that has 1g ginger extract in it
A teaspoon of fresh, grated, rhizome (the vertical aspect of ginger root)
2 droppers (2mL) of liquid extract
2 teaspoons (10mL) of syrup
4 cups (8 oz each) ginger tea, steeping 1/2 teaspoon grated ginger for 5–10 min
8-oz cup ginger ale, made with real ginger
2 pieces crystallized ginger, each 1 inch square, 1/4 inch thick