What is the process called that use to check each other's work?

Answer 1

Through peer review

Answer 2

Scientists repeat each others experiments to see if they get the same results.

This is why scientists write up papers to be published in scientific journals with very specific information about what they did in the experiment and the results they got. This lets other scientists verify the results by repeating the experiment.
By peer review

Answer 3

The most common way is to repeat the experiment. Some experiments are quite expensive to conduct, and in such cases, other scientists (peers) will review the work to confirm that the data fall within the expected ranges, or are consistent with their own results or the results of earlier experiments.

Most experiments must be repeated to be verified.

Another way of saying that is through peer review, although peer review generally consists of reviewing the assumptions, methodology, and data--NOT necessarily actually repeating the experiments.