My date was on 9th of last month but today on 8th i am having blood discharge is it mensuration or it is implantation bleeding?

Probable menses: Assuming you have a monthly flow, ovulation is approx day 15 and menses is approx day 28. A slight change in the flow can occasionally occur but if truly abnormal consider a pregnancy test. If on pill, did you miss any?

Do a pregnancy test: Even a home test should be positive if this represents "implantation" bleeding. A small amount of bleeding in early pregnancy is relatively common, but whether this truly reflects implantation is arguable.

Probably your period: If you are having regular cycles every 28-30 days, then the bleeding is probably your period and not implantation bleeding. There is, however, some women that will bleed around the time of their periods but are really pregnant. If you have any doubts, do a urine or blood pregnancy test to be sure. Hope this helps.