Genetic mutation can be caused by nucleotide alteration as a result of spontaneous or artificial mutation. Identifying the gene nucleotide (DNA or cDNA) of interest by sequencing can be a quick way of determining a mutation.
Definitely better to amplify the target region from gDNA with an high grade hi-fidelity polymerase and send the fragment for a forward and reverse strands Sanger sequencing.
RNAs are unstable themselves and even they should be converted into cDNA for sequencing, the cDNA synthesis is not high-fidelity as a proofreading TAQ.