Do I really have to find a cane ?

Yes you need to go to the clinic ask the doctor for the cane he will ask you for somehing in return go to the cobbler shope ask the aproperate question you recive the harness go the the fair wall you will see the cupboard on the wall click it there you will see differant canes I hope that this tip can help timothy

Go to the clinic and ask the doctor and he will say that someone gave it to him so they can pay for an oporation on his clients leg and the cane is worth a few coins and he asks if you can get him ajustable harnisses at the cobblers shop and he will give the cane to you but the hard bit is that you have to make the cane up again because it is in pieces I hope this helps

After you talk to Bella in the Brothel, talk to the artist behind you and he'll give a description of his cane. Also talk to the girl cleaning the floor and examine the shoe print she's trying to clean off the rug.
Go to the Clinic (northeast of Whitechapel) and examine the shoe print on the floor, near Dr. Gibbons. Talk to the doctor and he says he needs proof that this is the cane you're looking for.
Click on the cupboard at the back of the clinic and repair the cane. Use the Dialogues menu to figure out which parts to use. The top will be the roundish silver one, but with a pattern on it. The tip will also be the same. The middle part should be the part on the right side, that doesn't look like 3 rings. The cane is 1 of 3 black ones.
The doctor then requires harnesses as trade for the cane. Exit the Clinic, go southeast and enter the Cobbler's Shop. Inside, examine the harness on the table. Talk to the Jewish guy (Isaac) and he'll give you harnesses the next time you are in Whitechapel.