To find Salesforce Permission Label when we have API Name, we can make use of Schema.DescribeSObjectResult and Schema.DescribeFieldResult on PermissionSet object/entity.

Using the following code, we are finding the Label value of the PermissionsManageConvMiningReports Permission.

Sample Apex Code:

Schema.DescribeSObjectResult objectDescribeResult = 
    PermissionSet.sObjectType.getDescribe();  
Map < String , Schema.SObjectField > mapFieldList = 
    objectDescribeResult.fields.getMap();    

for ( 
    Schema.SObjectField field : 
    mapFieldList.values() 
) {    
  
    Schema.DescribeFieldResult fieldResult = 
        field.getDescribe(); 

    if ( 
        fieldResult.getName() == 'PermissionsManageConvMiningReports' 
    ) {

        System.debug(
            'Field Label is ' + 
            fieldResult.getLabel()
        );
        break;

    }
      
}