You can use the changeSets property of the currentBuild global variable to get information relating to the detected changes of the current build.
e.g.
// returns a list of changed files
@NonCPS
String getChangedFilesList() {
changedFiles = []
for (changeLogSet in currentBuild.changeSets) {
for (entry in changeLogSet.getItems()) { // for each commit in the detected changes
for (file in entry.getAffectedFiles()) {
changedFiles.add(file.getPath()) // add changed file to list
}
}
}
return changedFiles
}