If you're having the trouble finding The Medium tie clip, don't worry - finding Jack's tie clip is the first thing the game asks you to do, but it gives little or no guidance. Your only option is to walk around all the rooms in The Medium's opening level, looking for prompts in the hope that one of them might reveal the clip. To save you time and get things started quicker, here's where you can find the The Medium Tie clip.
The Medium tie clip location
The Medium tie clip is in Jack's room which is the left turn above, at the end of the corridor. When you get inside check the wall on the left to find a prompt that will let you examine a display of pins and medals.
While the wall of framed badges and pins are hard to miss it is easy to miss the smaller prompt below, on the shelf by the clock. This is the box where The Medium tie clip should be, but isn't. If you open you'll find it empty but as long as you actually notice it and interact with it you'll be okay - this triggers the tutorial for Insight, your spiritual instinct mode which will reveal Jack's tie clip is under the clock.
All you have to do now is interact with the clock to move it and you can grab The Medium tie clip and get out of the apartment to continue the game. While that's the only thing you need to do to proceed, there are plenty of other things you can do in the flat while you're there, like check out Marianne's room and feed the cat.