Hi Jia,
1. at RSA1--> Info provider---> right panel select your cube--> right click--> Manage, you can see content tab, there selective deletion icon will be there right side down,
click on delete selection, in next screen you can log, in that you can see who performed selective deletion on perticular cube.
Even at SM37, give job name as BI_INDEX*, user id: *
select status - Finished and active, you will get all jobs which are related to selective deletion on all targets.
2 & 3.
At dso or cube , rigth click--> manage, there you can see request tab, there is column Load Monitor, if you choose respective monitor, that moniter will show details who ran that DTP in header tab. there is a userid.
4. Viwing data thru bex query then you can check this table - RSDDSTAT_OLAP. its contains bexy query history. even by using RSRT also you can get.
Table name - RSDDSTAT_OLAP., there is field Query ID, there you can pass Query technical name.
Thanks