You have a cascade of errors but all starts here
ERROR: failed to lock directory ‘/home/gjk/R/x86_64-pc-linux-gnu-library/3.6’ for modifying
Try removing ‘/home/gjk/R/x86_64-pc-linux-gnu-library/3.6/00LOCK-Rcpp’
Follow the indication on the error message and delete that file, then try to install again.
Also, for future posts, is better if you post the error message here directly as formatted code