Most damaged SIM-readers can be determined broken without disassembling the device. If the SIM problem persists despite external signs of damage, disassembling the device is in order.

Follow the steps in the P6 motherboard replacement guide Huawei Ascend P6-U06 Motherboard Replacement to disassemble the device. At this point, you should have a good view inside the sim slot.

Inspect the reader's contidition - preferably using a microscope, or at least a jeweler's loupe - poking at the contacts to see if anything is loose.

You can also measure continuity between the points marked in the crude schematic, however, this only tells you whether the motherboard is functional regarding the SIM ways.

At this point either there should be sightings of missing/bent pins inside the SIM reader, or the pads measure incorrectly, otherwise this guide can be potenionally making the problem worse.