To operate CW with FTDX10 via USB using N1MM logger you need to install the virtual COM drivers, change radio settings and configure N1MM.
Virtual COM port drivers
Change radio settings
On your FTDX10 press the FUNC knob, select CW settings, select MODE CW and under PC Keying select RTS.
Press Back to exit this menu, then select Operation Settings, select General then select the CAT rate (mine is 4800). This value must be selected in the N1MM settings (below).