HP 11-G5 11.6" Intel Dual-Core Chromebook

can you add memory?

Seems not, per specs.
Memory: Your Choice:
2GB DDR3 (on-board, non-expandable)
4GB DDR3 (on-board, non-expandable)

Does it have ethernet RJ-45?

Yes it does, all Chromebooks have rj45. One of the standards that Google imposes on all manufacturers.

Does this have a card reader?

Does this have a SD card slot?