(∩ ͡⎚ ͜ʖ ͡⎚)⊃━☆ﾟ.* Here we go!
Problems:
I'll point out some of the mistakes that bug me the most here, then I'll tell you my opinion about the concept.
in a 50cm x 50cm x 50cm
10m x 10m x 5m
A common mistake. Actually, if the size of the chamber isn't very important for the containment, you don't need to specify it. Just write "in a standard chamber" instead.
Description
SCP-XXXX
By the way, the formatting is weird here. Should be "Description: [TEXT]". Same with the Containment procedures.
SCP-XXXX appears to be a standard household kitchen knife
Why not just "SCP-XXXX IS a standard household kitchen knife"? I've pointed it out because that's also the common misconception regarding clinical tone: you don't need to make sentences as long as possible to make them look more clinical, you just need to describe your object as clear as possible.
(Now classified as SCP-XXXX-1)
Word "classified" has a different meaning. Probably you meant "designated as SCP-XXXX-1".
SCP-XXXX seems to actually transfer its conscience
This assumption is based on nothing. The fact that the victim starts to insult everyone around them doesn't mean that SCP-XXXX itself is sapient. It could be just another compulsion effect that makes it's victims behave like this.
Now, there are more issues with formatting and wording, but let's just jump to the concept critique because I feel like it's very important.
The concept, as of right now, looks very weak and uninteresting. You have a knife which makes people violently kill other people. That's one of the overdone cliches in SCP, called "compulsion effect", also the anomaly itself is very generic. And I'm not telling you that it is impossible to make this cliche work, but you need far more than just the thing that does bad things to make it an interesting read. My advice here would be to focus more on the story, than the anomaly itself. For example, take a look at SCP-3041.
Regarding the structure: The first Addendum looks strange and random, I don't fully understand what you were trying to say with it. The testing is… Fine, but it doesn't really bring anything new to the table, other than the fact that SCP-XXXX-1 will insult everyone in the process. And the final addendum is… Meh, it says SCP-XXXX is sapient, but I don't see any confirmation of it, so it doesn't work. When writing an SCP, you should make Foundation's in-universe assumptions believable enough to not break reader's immersion.
How to solve them?
Also, I understand that English isn't your first language. I'm here too. English is, in fact, my third language. So, there are some links that may help you with your clinical tone if you have problems with it:
http://www.aje.com/en/arc/editing-tip-maintaining-formal-tone-scientific-writing/
http://academicguides.waldenu.edu/writingcenter/scholarlyvoice/tone
https://healthcare.utah.edu/brand-and-style-guide/writing-guide.php
http://vrici.lojban.org/~cowan/style-revised.html
(∩ ͡° ͜ʖ ͡° )⊃━☆ﾟ.* Feedback is over, good luck!
