That depends on which point in a comet's orbit you are talking about.
The Earth's orbital velocity is about 30 kilometers/sec, so that
comets that get as close to the Sun as the Earth's orbit can be traveling at
least this fast. If a body 'falls' from beyond the orbit of Pluto and passes
the Earth without being captured by the Sun, it is probably traveling
closer to 50 kilometers/sec. In the most distant parts of its orbit it could
be traveling as slowly as a few kilometers/sec.
