I have "X" gene my interest which expressed significantly in Y tissue. Can I predict the function of gene "X" by performing gene ontology enrichment analysis on genes whose expression are significantly co-related with gene X in the Y tissue?
If it is protein coding, the functions can be predicted by its protein ( not a appropriate way though). To make it more reliable you please check the answer below.
If you are talking about non-coding RNA (also applicable for protein coding). The ideal thing will be knocking down (kd) the gene 'X' in the cells related to your tissue type using siRNA or shRNA and do the enrichment analysis for the genes that are affected by Gene 'X' kd. This will give you idea on functions or pathways affected by your gene 'X'.
There might be other ways to do that I am missing here.