There are 2 errors here, the first is that it's unable to locate your nodes6.csv file, to me it looks like you entered the file name with an extra ,
.
What you have:
java -server -Xmx4G -jar target/batch-import-jar-with-dependencies.jar target/db nodes6.csv, rels5.csv
Should it be this: java -server -Xmx4G -jar target/batch-import-jar-with-dependencies.jar target/db nodes6.csv rels5.csv