The basics: current is measured with an ammeter in units called amperes (amps for short). You will want to look at continuous and peak amp performance specs for the particular model you are interested in. It is important to discuss this issue with the speaker manufacturer as well. They should be able to provide you with a guideline as to what will do the job.
Then you should be able to get started on selecting an amp that will not only have enough current to drive the speaker, but also sound good in the process.
Then you should be able to get started on selecting an amp that will not only have enough current to drive the speaker, but also sound good in the process.