Pritpal - you can't get a h-index of an individual study. A h-index is a score of multiple studies multiplied i.e. a h-index of 20 indicates 20 studies that have all been cited more than 20 times each. The likes of Scimago will tell you the 'collective' h-index for journals - but not for individual publications within them.
Pritpal - I do't think there is any metric by researchers can calculate the 'h- index' of each publication. The index is based on a list of publications ranked in descending order by the number of citations these publications received. The value of h is equal to the number of papers (N) in the list that have N or more citations. Before you can calculate your h-index, you will need a complete publication list. The h-index is calculated by counting the number of publications for which an author has been cited by other authors at least that same number of times. Keep in mind that different databases will give different values for the h-index. This is because each database must calculate the value based on the citations it contains. Since databases cover different publications in different ranges of years, the h-index result will therefore vary. Also, what is considered a "good" h-index may differ depending on the scientific discipline. A number that is considered low in one field might be considered quite high in another field.