Can i split the coax cable going to my cable modem to attach a TV there ?
Usually yes, however it is not a good idea to do so. Every splitter on the cable between the can and your cable modem reduces signal strength (by at least 3db). Also, mistakes in home wiring can cause ingress in the upstream channel for all users on that upstream.
If you must split the cable going to your cable modem, you should use either a tap (loss only on one end, going to your TV), or high grade 2GHz splitters, and because of the lower signal level the modem might not synch at all, or you might experience some packet loss and speed degradation. Depending on your installation, there also might be some filters on the line preventing the operation of both TV and the cable modem on the same cable.
Notes: It may be a good idea to check the signal strength on your cable modem to determine whether a tap or a splitter is better for you - a tap will only incur signal degradation on one leg (-6db), while a splitter will incur signal degradation on both legs (-3.5db).