Should I do another PhD? I have completed my PhD in chemistry in an area which doesn’t have scope to get job or a postdoc position. 

Now I’m at the age of 29–30, I’m not eligible to write CSIR, a public eligibility test for lectureship and PhD admissions in India, but I’m eligible to write GATE-2016, (Graduate Aptitude Test for Engineering) another public test whose score (valid for 2 years) is also considered for PhD admissions in India and some other countries like Singapore. Shall do another PhD with a valued GATE score again, in my selected field of chemistry?
The only stipend available for me is from GATE score.
It is not possible to give a concrete answer without knowing which area in Chemistry you did for your PhD. I assume you are from India. There are other options for you to consider irrespective of your field of research.


Try to get an INSPIRE Faculty position, which is not really a faculty position in usual sense.
Apply abroad which will increase your chance of finding a similar field at least statistically.


I don't think appearing GATE once again is a good idea. Also why don't you try industry, there are plenty of jobs for chemists, once again its hard to say for sure without knowing your area of research.