I am just trying to shorten a clip and insert a crossfade in the middle without a corresponding volume dip.   Have looked at all the documentation online and can't find a solution. When you search the documentation, seems you are more likely to find help for X2 and X3 than anything current. I am sure that I am missing something obvious.   Have been a cakewalk/sonar user for 20 years and have crossfaded many clips but this version of Sonar has me baffled.
 
Sonar Pro - updated to latest version available

Auto crossfade is "checked" under options. 

been a long time since I did a cross fade in Sonar. typically I only do fades (singular).
so bare with me.
Place the now time to where you want the crossfade, right click and check the options. I though it was under split options but not sure if that makes much sense.

I'm not sure what you mean by "in the middle". If you mean between two clips and bringing them together you can use automatic crossfades. 
 
Below is from page 730 of the Sonar manual.
Fades and crossfades
Fades are a gradual increase or decrease in volume at the beginning (fade-in) or end (fade-out) of a clip. A
crossfade is when one clip fades out while another fades in. There are two ways to create fades and crossfades in
SONAR: offline (destructive) and real-time (non-destructive). To create fades and crossfades offline, see
“Applying fades and crossfades offline” on page 1189.
See:
“Using fades and crossfades in real-time” on page 730
Using fades and crossfades in real-time
You can create real-time fades and crossfades in the Track view’s Clips pane. Real-time fades and crossfades do
not change the data in the clip. SONAR reads the fade-in, fade-out, or crossfade in the clip and adjusts the gain
accordingly. You can edit the crossfade’s start time and end times. You can set the type of fade-in or fade-out you
want to use as a default:
Linear. A straight line, raising or lowering the volume at a steady rate.
Slow Curve. A curved fade which starts to change the volume slowly at first and then rapidly increasing
(fade-in) or decreasing (fade-out) the volume.
Fast Curve. A curved fade which starts to change the volume quickly at first and then rapidly decreasing
(fade-out) or increasing (fade-in) the volume.
To choose the fade type
Click the Track view Options menu, point to Crossfade Type and select the desired default Fade-In, Fade-Out
and Crossfade curve types.
To create a real-time fade-in in a Clip
1. Select the Smart tool or Edit tool in the Control Bar.
2. In the Track view’s Clips pane, move your mouse over the top part of the beginning of a clip until the cursor
looks like this: , and a red line appears at the edge of the clip.
A filled red triangle appears at the top of the red line indicating the fade marker is ready to be dragged.
A. Filled red triangle
A

Like John, I'm not sure what the intent of inserting a crossfade in the middle of single clip is...? Usually a crossfade is between two clips.
 
In any case, there are basically three ways to create a crossfade:
 
1. With lanes not showing, split the clip and drag one half to overlap the other with Auto-crossfades enabled in Track View options (should be by default).
 
2. As above, but slip edit one side of the split to overlap the other without moving the clips.
 
3. Show take lanes (Shift+T) and swipe in the bottom half of the clip with the Comp tool to split out a section of the clip that will be automatically crossfades 'with itself' at either end of the section. If you swipe from within the clip to somewhere beyond either end, you'll just get the one crossfade where you started. The default width of the Comping crossfade is detemined by a setting in Preferences > Customization > Editing, but you can hod Ctrl+click and drag up and down on the crossfade to adjust the width.
 
If you meant 'fade in' or 'fade out' rather than crossfade, just hover over the upper corner of the clip to get the clip fade tool and drag to create the fade. The red fade handle/marker that used to appear has disappeared in favor of a fade tool icon.

Ya, this is total word salad. Try again.