Elemental　doping　is　widely　used　to　improve　the　performance　of　cathode　materials　in　lithium-ion　batteries.　However,　macroscopic/statistical　investigation　on　how　doping　sites　are　distributed　in　the　material　lattice,　despite　being　a　key　prerequisite　for　understanding　and　manipulating　the　doping　effect,　has　not　been　effectively　established.　Herein,　to　solve　this　predicament,　a　universal　strategy　is　proposed　to　quantitatively　identify　the　locations　of　Al　and　Mg　dopants　in　lithium-rich　layered　oxides　(LLOs).　Solid　evidence　confirms　that　Al　prefers　to　occupy　the　transition　metal　(TM)　layer,　while　Mg　evenly　occupies　both　TM　and　Li　layers.　As　a　result,　Mg　significantly　reduces　the　thickness　of　LiO2　slabs　at　room　temperature,　which　will　increase　the　energy　barrier　of　oxygen　activation　and　enhance　the　structure　stability　of　LLOs.　The　suppressed　oxygen　activity　in　Mg-doped　LLO　can　be　kinetically　unlocked　at　55　degrees　C.　The　different　characteristics　of　Al　and　Mg　enlighten　an　Al/Mg　co-doping　strategy　to　optimize　LLOs,　which　significantly　improves　the　cycle　performance　while　lifting　the　capacity.　These　insights　from　the　quantitative　identification　of　doping　sites　shed　light　on　the　manipulation　of　doping　effects　toward　better　cathodes.