Database
[{"_id":{"monthDate":"04-03-2020"},"Job":["Designer","Tester","Designer"]},{"_id":{"monthDate":"14-03-2020"},"Job":["Designer","Tester","Tester"]},{"_id":{"monthDate":"24-03-2020"},"Job":["Developer","Manager"]},{"_id":{"monthDate":"25-03-2020"},"Job":["Developer","Developer","Developer"]}]
Query
db.collection.aggregate([{$addFields:{Job:{$arrayToObject:{$map:{input:{$setUnion:"$Job"},as:"j",in:{k:"$$j",v:{$size:{$filter:{input:"$Job",cond:{$eq:["$$this","$$j"]}}}}}}}}}}])