user11629: In the following example (and similar situations you can make up), both queens can capture the knight. If for instance the queen on f5 takes the knight, this could be written as: Qfxd3 or as Q5xd3. Is there a preference/guideline/law/... for using one or the other notation in this case? I am specifically interested in notations made by humans in a normal game situation, not in PGN notation.
8/8/8/5Q2/8/3n4/4Q3/8 w - - 1 1


user12540: Chess Board is divided into 1-8 ranks and a-h files .
Generally this problem arises with Rooks & Knights .
When two Queens standing on two different Squares and have one common attacking Square or same Piece then we use for convenience 
Q Square number * Square number . 
Here it would be either Qf5*d3 or Qe2*d3 .
Any of the 64 Squares can be represented with the File + Rank convention . Always use the initial & final square number for better representation & avoiding ambiguity .

user-1: This would be Qfxd3.
From wikipedia (emphasis is mine):

When two (or more) identical pieces can move to the same square, the moving piece is uniquely identified by specifying the piece's letter, followed by (in descending order of preference):

the file of departure (if they differ); or
the rank of departure (if the files are the same but the ranks    differ); or
both the file and rank (if neither alone is sufficient to identify    the piece—which occurs only in rare cases where one or more pawns
  have promoted, resulting in a player having three or more identical
  pieces able to reach the same square).



11629: <p>In the following example (and similar situations you can make up), both queens can capture the knight. If for instance the queen on f5 takes the knight, this could be written as: Qfxd3 or as Q5xd3. Is there a preference/guideline/law/... for using one or the other notation in this case? I am specifically interested in notations made by humans in a normal game situation, not in PGN notation.</p>

<pre><code>8/8/8/5Q2/8/3n4/4Q3/8 w - - 1 1
</code></pre>
 12540: <p>Chess Board is divided into 1-8 ranks and a-h files .</p>

<p>Generally this problem arises with Rooks &amp; Knights .</p>

<p>When two Queens standing on two different Squares and have one common attacking Square or same Piece then we use for convenience </p>

<p>Q Square number * Square number . </p>

<p>Here it would be either Qf5*d3 or Qe2*d3 .</p>

<p>Any of the 64 Squares can be represented with the File + Rank convention . Always use the initial &amp; final square number for better representation &amp; avoiding ambiguity .</p>
 -1: <p>This would be <strong>Qfxd3</strong>.</p>

<p>From <a href="https://en.wikipedia.org/wiki/Algebraic_notation_(chess)#Disambiguating_moves" rel="noreferrer">wikipedia</a> (emphasis is mine):</p>

<blockquote>
  <p>When two (or more) identical pieces can move to the same square, the moving piece is uniquely identified by specifying the piece's letter, followed by (<strong>in descending order of preference</strong>):</p>
  
  <ul>
  <li>the <strong>file</strong> of departure (if they differ); or</li>
  <li>the rank of departure (if the files are the same but the ranks    differ); or</li>
  <li>both the file and rank (if neither alone is sufficient to identify    the piece—which occurs only in rare cases where one or more pawns<br>
  have promoted, resulting in a player having three or more identical<br>
  pieces able to reach the same square).</li>
  </ul>
</blockquote>
