You can always view the latest known price on Pepins. On this page, you will find all companies on Pepins offering trade. You can view the latest known price, and when the most recent transaction was made. You can also click into each company to view the share price development over time, and the transactions completed.
If the company has not yet offered trade, the price is most likely the same as the acquisition value.
You can view the latest price on each of your share positions, under "My Pepins".