Do you mean in vitro, then you could do a PCR.

If you have sequencing read, you could use a tool for genomic datasets: https://genomebiology.biomedcentral.com/articles/10.1186/s13059-015-0849-0

In other cases and if you have read pairs, you might just look at read pairs confirming the circularity (if mapped uniquely).

thanks Thomas.D.Otto jee for kind reply. 

This tool is applicable in case of reads generated through Pacific Biosciences and Oxford Nanopore. Can you suggest any tool that do same work using  reads generated through illumina/solexa.

This paper describes a computational pipeline for discovering circularity in Illumina and 454 reads.

http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0087924

This is what i was looking for.

Thanks Matej Lexa

there are also a few tools for circular RNA detection (though you librarary should be treated with RNase R before hand to be meaningfull). CIRI, findCIRC, CIRCexplorer and so on: https://omictools.com/circular-rna-detection-category