The postmark is Danby type B(c) squared circle cancel of Lakhnau GPO (est. 1801), located in Lakhnau (26.8467°N 80.9462°E), now in Lakhnau district of Uttar Pradesh state.
Lakhnau was the capital of erstwhile Indian Feudatory State Avadh and now the capital of UP state.
Type B(c) did have 2 digit year below the month and date.
Since it is not impressed clearly on the stamp, it can be systematically deduced.
1. The fleuron at the base of the circle appeared in Danby type B(c) cancels only in 1889.
2. The latest recorded date of type B(c) cancel of Lakhnau is Jul 1890.
3. The stamp is Br. India 1890 3A brown orange SG 94.
So, it can safely be assumed that the year in the cancel is 1890.