Indeed it needs practice and thoughtful estimation for injecting cDNA into the nucleus of Xenopus oocyte cell. How to access nicely injecting cDNA into the nucleus of oocyte?
Claudio provides nice experimental tests for checking that your injection construct is expressed. As a means to simply check if you are indeed injecting into the nucleus (vs cytoplasm), you could coinject an inert dye, such as 1% methylene blue.