Please follow the following transformations:
a) Tu conosci il fatto che io non sento bene ?
il fatto ==> lo (object pronoun)
conoscere ==> sapere
b) Tu lo sai che io non sento bene ?
Now: drop the subject pronouns, as they are impl;icit from the verbal voice
c) lo sai che non sento bene ?
Turn on a global object for /sentire/ meaning a physical condition related to the subject; in this case /ci/ is a substitude for a /global context/ related to /to hear/.
d) lo sai che non CI sento bene ?
See the difference with a specialized object:
e1) lo sai che non sento bene il suono del telefono ?
e2) lo sai che non sento bene la musica ?
(e1) andd (e2) do not speak about an intrinsic condition of the subject, related to the action of /to hear/.
(c) is also ok, but (d) is better!
remember:
/sentire/ has two tanslations with DIFFERENT meanings:
to hear
to feel
(obviously here is /to hear/)