Car was shifing fine...now is stuck in second gear. Clutch will engage...but no other gear is selectable. ...no strange noises...just will not shift. ...possible linkage problem? How difficult of a fix is this?

this manual transmission?
seems. so
the tip of shift levers love to get worn and not allowing the shift rail forks to hit 3rd gear.
a pure simple mechanical failure and is shifter tip end parts bad, some are even made of plastic.
or
3rd gear synchro- ring is super worn out and the main clutch drags. (seen it and fixed them)
if clutch has master cylinder is the fluid always at top line or drops in time every weak.

Time to find a transmission or someone to rebuild it.

although clutch may feel like it is engaging i suspect the pressure plate is worn ,if you try to engage gears with engine running is there a grating noise ?

bad pressure plate or stuck throw out bearing.

YEP SHIFT LINKAGE LOOSE OR WORN NEED ADJUSTMENT.ADJUST THE SHIFT LINKAGE BY POSITION THE SHIFT LEVER IN NEUTRAL .REMOVE THE REAR TUNNEL COVER IN FRONT OF THE REAR SEAT.PULL THE RUBBER DUST COVER FORWARD ON THE SHIFT ROD.LOOSEN THE CLAMP BOLT ON THE SHIFT ROD.MOVE THE TRANSMISSION SELECTOR SHAFT ALL THE ITS LEFT STOP,KEEPING IT IN NEUTRAL.WITH THE TRANSMISSION STILL IN NEUTRAL . MOVE THE GEARSHIFT ROD TO THE RIGHT TO ITS STOP.TIGHTEN THE CLAMP BOLT TO 18 FT LBS.TEST THE SHIFT LEVER PLAY SHOULD BE THE SAME IN ALL GEARS IN ALL DIRECTIONS.

sounds like your clutch is going out, is it hard to put in gear with clutch all the way depressed? could also be the sinkronyzer going out, could be the gears in the transmission also going bad. need to check the fluid in the transmission.

Go to Trans repair shop NOW!! Major electromechanical problems are present starting with too high of internal line pressure causing harsh gear engagement, the second concern is your 1st gear clutch pack will not apply or there is major internal damage.

I'm sorry for the bad news..

Hi my mazda etude 160i the left wheel gets stuck and it give a knocking sound.then its free again.I checked the CV but thats fine.

Usually this is a linkage problem, and most often the rubber lined coupling between two rods in the linkage system. This fails as the rubber ages, and when it does you are unable to select some or all gears, and might be stuck in one gear!

Not too difficult to re and re, and part is available from Saab dealer at reasonable cost.

Coupling may be located inside the car, under the console, ahead of the gear lever housing, or on the other side of the firewall